diff --git a/EESSI-install-software.sh b/EESSI-install-software.sh
index 713fcba883..099050b276 100755
--- a/EESSI-install-software.sh
+++ b/EESSI-install-software.sh
@@ -242,8 +242,8 @@ fi
 # order is important: these are needed to install a full CUDA SDK in host_injections
 # for now, this just reinstalls all scripts. Note the most elegant, but works
 
-# Only run install_scripts.sh if not dev.eessi.io for security
-if [[ "${EESSI_CVMFS_REPO}" != /cvmfs/dev.eessi.io ]]; then
+# Only run install_scripts.sh if not in dev.eessi.io for security
+if [[ -z ${EESSI_DEV_PROJECT} ]]; then
     ${TOPDIR}/install_scripts.sh --prefix ${EESSI_PREFIX}
 fi
 
@@ -268,8 +268,19 @@ export EESSI_CVMFS_INSTALL=1
 # NOTE 3, we have to set a default for EASYBUILD_INSTALLPATH here in cases the
 #   EESSI-extend module itself needs to be installed.
 export EASYBUILD_INSTALLPATH=${EESSI_PREFIX}/software/${EESSI_OS_TYPE}/${EESSI_SOFTWARE_SUBDIR_OVERRIDE}
+
+# If in dev.eessi.io, allow building on top of software.eessi.io via EESSI-extend
+if [[ ! -z ${EESSI_DEV_PROJECT} ]]; then
+    # We keep track of the old install path for settings paths to SitePackage.lua and .lmodrc later
+    EASYBUILD_INSTALLPATH_STANDARD=${EASYBUILD_INSTALLPATH}
+    # Need to unset $EESSI_CVMFS_INSTALL to use $EESSI_PROJECT_INSTALL
+    unset EESSI_CVMFS_INSTALL
+    export EESSI_PROJECT_INSTALL=${EESSI_CVMFS_REPO_OVERRIDE}
+    echo ">> \$EESSI_PROJECT_INSTALL set to ${EESSI_PROJECT_INSTALL}"
+fi
+
 echo "DEBUG: before loading EESSI-extend // EASYBUILD_INSTALLPATH='${EASYBUILD_INSTALLPATH}'"
-source load_eessi_extend_module.sh ${EESSI_VERSION}
+source $TOPDIR/load_eessi_extend_module.sh ${EESSI_VERSION}
 echo "DEBUG: after loading EESSI-extend //  EASYBUILD_INSTALLPATH='${EASYBUILD_INSTALLPATH}'"
 
 # Install full CUDA SDK and cu* libraries in host_injections
@@ -319,11 +330,6 @@ if [ ! -z ${EESSI_ACCELERATOR_TARGET} ]; then
     fi
 fi
 
-# If in dev.eessi.io, allow building on top of software.eessi.io
-if [[ "${EESSI_CVMFS_REPO}" == /cvmfs/dev.eessi.io ]]; then
-    module use /cvmfs/software.eessi.io/versions/$EESSI_VERSION/software/${EESSI_OS_TYPE}/${EESSI_SOFTWARE_SUBDIR_OVERRIDE}/modules/all
-fi
-
 echo "DEBUG: adding path '$EASYBUILD_INSTALLPATH/modules/all' to MODULEPATH='${MODULEPATH}'"
 #module use $EASYBUILD_INSTALLPATH/modules/all
 safe_module_use $EASYBUILD_INSTALLPATH/modules/all
@@ -396,7 +402,15 @@ else
 fi
 
 echo "DEBUG: before creating/updating lmod config files // EASYBUILD_INSTALLPATH='${EASYBUILD_INSTALLPATH}'"
-export LMOD_CONFIG_DIR="${EASYBUILD_INSTALLPATH}/.lmod"
+if [[ ! -z ${EESSI_DEV_PROJECT} ]]; then
+    # Make sure .lmod files are not checked for dev.eeessi.io
+    export LMOD_CONFIG_DIR="${EASYBUILD_INSTALLPATH_STANDARD}/.lmod"
+    export LMOD_PACKAGE_PATH="${EASYBUILD_INSTALLPATH_STANDARD}/.lmod"
+else
+    export LMOD_CONFIG_DIR="${EASYBUILD_INSTALLPATH}/.lmod"
+    export LMOD_PACKAGE_PATH="${EASYBUILD_INSTALLPATH}/.lmod"
+fi
+
 lmod_rc_file="$LMOD_CONFIG_DIR/lmodrc.lua"
 echo "DEBUG: lmod_rc_file='${lmod_rc_file}'"
 if [[ ! -z ${EESSI_ACCELERATOR_TARGET} ]]; then
@@ -411,7 +425,6 @@ if [ ! -f $lmod_rc_file ] || [ ${lmodrc_changed} == '0' ]; then
     check_exit_code $? "$lmod_rc_file created" "Failed to create $lmod_rc_file"
 fi
 
-export LMOD_PACKAGE_PATH="${EASYBUILD_INSTALLPATH}/.lmod"
 lmod_sitepackage_file="$LMOD_PACKAGE_PATH/SitePackage.lua"
 if [[ ! -z ${EESSI_ACCELERATOR_TARGET} ]]; then
     # EESSI_ACCELERATOR_TARGET is set, so let's remove the accelerator path from $lmod_sitepackage_file
diff --git a/bot/build.sh b/bot/build.sh
index 2b35c63551..2bba0cba55 100755
--- a/bot/build.sh
+++ b/bot/build.sh
@@ -147,7 +147,9 @@ echo "bot/build.sh: EESSI_VERSION_OVERRIDE='${EESSI_VERSION_OVERRIDE}'"
 # determine CVMFS repo to be used from .repository.repo_name in ${JOB_CFG_FILE}
 # here, just set EESSI_CVMFS_REPO_OVERRIDE, a bit further down
 # "source init/eessi_defaults" via sourcing init/minimal_eessi_env
-export EESSI_CVMFS_REPO_OVERRIDE=/cvmfs/${REPOSITORY_NAME}
+# Note: iff ${EESSI_DEV_PROJECT} is defined (building for dev.eessi.io), then we 
+# append the project subdirectory to ${EESSI_CVMFS_REPO_OVERRIDE}
+export EESSI_CVMFS_REPO_OVERRIDE=/cvmfs/${REPOSITORY_NAME}${EESSI_DEV_PROJECT:+/$EESSI_DEV_PROJECT}
 echo "bot/build.sh: EESSI_CVMFS_REPO_OVERRIDE='${EESSI_CVMFS_REPO_OVERRIDE}'"
 
 # determine CPU architecture to be used from entry .architecture in ${JOB_CFG_FILE}
@@ -318,7 +320,15 @@ fi
 timestamp=$(date +%s)
 # to set EESSI_VERSION we need to source init/eessi_defaults now
 source $software_layer_dir/init/eessi_defaults
-export TGZ=$(printf "eessi-%s-software-%s-%s-%d.tar.gz" ${EESSI_VERSION} ${EESSI_OS_TYPE} ${EESSI_SOFTWARE_SUBDIR_OVERRIDE//\//-} ${timestamp})
+# Note: iff ${EESSI_DEV_PROJECT} is defined (building for dev.eessi.io), then we 
+# append the project (subdirectory) name to the end tarball name. This is information
+# then used at the ingestion stage. If ${EESSI_DEV_PROJECT} is not defined, nothing is
+# appended
+export TGZ=$(printf "eessi-%s-software-%s-%s-%b%d.tar.gz" ${EESSI_VERSION} ${EESSI_OS_TYPE} ${EESSI_SOFTWARE_SUBDIR_OVERRIDE//\//-} ${EESSI_DEV_PROJECT:+$EESSI_DEV_PROJECT-} ${timestamp})
+
+# Export EESSI_DEV_PROJECT to use it (if needed) when making tarball
+echo "bot/build.sh: EESSI_DEV_PROJECT='${EESSI_DEV_PROJECT}'"
+export EESSI_DEV_PROJECT=${EESSI_DEV_PROJECT}
 
 # value of first parameter to create_tarball.sh - TMP_IN_CONTAINER - needs to be
 # synchronised with setting of TMP_IN_CONTAINER in eessi_container.sh
diff --git a/bot/inspect.sh b/bot/inspect.sh
index 533968bffc..6ffd227b59 100755
--- a/bot/inspect.sh
+++ b/bot/inspect.sh
@@ -209,7 +209,7 @@ echo "bot/inspect.sh: EESSI_VERSION_OVERRIDE='${EESSI_VERSION_OVERRIDE}'"
 # determine CVMFS repo to be used from .repository.repo_name in ${JOB_CFG_FILE}
 # here, just set EESSI_CVMFS_REPO_OVERRIDE, a bit further down
 # "source init/eessi_defaults" via sourcing init/minimal_eessi_env
-export EESSI_CVMFS_REPO_OVERRIDE="/cvmfs/$(cfg_get_value 'repository' 'repo_name')"
+export EESSI_CVMFS_REPO_OVERRIDE="/cvmfs/$(cfg_get_value 'repository' 'repo_name')${EESSI_DEV_PROJECT:+/$EESSI_DEV_PROJECT}"
 echo "bot/inspect.sh: EESSI_CVMFS_REPO_OVERRIDE='${EESSI_CVMFS_REPO_OVERRIDE}'"
 
 # determine architecture to be used from entry .architecture in ${JOB_CFG_FILE}
diff --git a/create_tarball.sh b/create_tarball.sh
index 01f498e1ac..bae66fb836 100755
--- a/create_tarball.sh
+++ b/create_tarball.sh
@@ -20,15 +20,18 @@ echo ">> tmpdir: $tmpdir"
 os="linux"
 source ${base_dir}/init/eessi_defaults
 cvmfs_repo=${EESSI_CVMFS_REPO}
-
 software_dir="${cvmfs_repo}/versions/${eessi_version}/software/${os}/${cpu_arch_subdir}"
 if [ ! -d ${software_dir} ]; then
     echo "Software directory ${software_dir} does not exist?!" >&2
     exit 2
 fi
 
-cvmfs_repo_name=${cvmfs_repo#/cvmfs/}
-overlay_upper_dir="${eessi_tmpdir}/${cvmfs_repo_name}/overlay-upper"
+# Need to extract the cvmfs_repo_name from the cvmfs_repo variable
+# - remove /${EESSI_DEV_PROJECT} from the end (if it exists)
+# - remove /cvmfs/ from the beginning
+cvmfs_repo_name=${cvmfs_repo%"/${EESSI_DEV_PROJECT}"}
+cvmfs_repo_name=${cvmfs_repo_name#/cvmfs/}
+overlay_upper_dir="${eessi_tmpdir}/${cvmfs_repo_name}/overlay-upper${EESSI_DEV_PROJECT:+/$EESSI_DEV_PROJECT}"
 
 software_dir_overlay="${overlay_upper_dir}/versions/${eessi_version}"
 if [ ! -d ${software_dir_overlay} ]; then
diff --git a/eessi_container.sh b/eessi_container.sh
index d96ad041a8..906eb2cbc2 100755
--- a/eessi_container.sh
+++ b/eessi_container.sh
@@ -763,6 +763,8 @@ do
         cfg_repo_id=${cvmfs_repo_name}
         cvmfs_repo_name=$(cfg_get_value ${cfg_repo_id} "repo_name")
     fi
+    # remove project subdir in container
+    cvmfs_repo_name=${cvmfs_repo_name%"/${EESSI_DEV_PROJECT}"}
 
     # always create a directory for the repository (e.g., to store settings, ...)
     mkdir -p ${EESSI_TMPDIR}/${cvmfs_repo_name}
@@ -812,8 +814,9 @@ do
         fi
     elif [[ ${cvmfs_repo_access} == "rw" ]] ; then
         # use repo-specific overlay directories
-        mkdir -p ${EESSI_TMPDIR}/${cvmfs_repo_name}/overlay-upper
-        mkdir -p ${EESSI_TMPDIR}/${cvmfs_repo_name}/overlay-work
+        mkdir -p ${EESSI_TMPDIR}/${cvmfs_repo_name}/overlay-upper${EESSI_DEV_PROJECT:+/$EESSI_DEV_PROJECT}
+        mkdir -p ${EESSI_TMPDIR}/${cvmfs_repo_name}/overlay-work${EESSI_DEV_PROJECT:+/$EESSI_DEV_PROJECT}
+
         [[ ${VERBOSE} -eq 1 ]] && echo -e "TMP directory contents:\n$(ls -l ${EESSI_TMPDIR})"
 
         # set environment variables for fuse mounts in Singularity container
diff --git a/run_in_compat_layer_env.sh b/run_in_compat_layer_env.sh
index b4299c7a0d..e9a49cbe3d 100755
--- a/run_in_compat_layer_env.sh
+++ b/run_in_compat_layer_env.sh
@@ -35,6 +35,9 @@ fi
 if [ ! -z ${EESSI_CVMFS_REPO_OVERRIDE} ]; then
     INPUT="export EESSI_CVMFS_REPO_OVERRIDE=${EESSI_CVMFS_REPO_OVERRIDE}; ${INPUT}"
 fi
+if [ ! -z ${EESSI_DEV_PROJECT} ]; then
+    INPUT="export EESSI_DEV_PROJECT=${EESSI_DEV_PROJECT}; ${INPUT}"
+fi
 if [ ! -z ${EESSI_VERSION_OVERRIDE} ]; then
     INPUT="export EESSI_VERSION_OVERRIDE=${EESSI_VERSION_OVERRIDE}; ${INPUT}"
 fi