Registry, and extract from installers

[Ra2-IFV]

How to extract from innosetup installers?

I checked here but didn't see much information. There's a key called innosetup but doesn't tell what happens if I fill url with installer link and set it to true. And, how about msi installers? how to extract them?

What's the recommended way to setup registry?

The installer writes something to registry ( in iss script ), I use reg command in post install scripts, is there a recommended way for this?
Writing to registry requires admin privileges, what if I don't install it globally?

Thanks for upir kindness. I searched issues and discussions and didn't find anything useful, or I am just too careless.