Just to make it clear:
Extracting the setup script with Unniversal Extractor (And, for the matter, with InnoUnp), is useless.
After re-compiling everything from a extracted .ISS file in these ways, it'll become the "always-simple" Inno Setup installer, with
no autorun menu,
no FreeArc + PreComp + Srep extraction support,
no pretty pages (
the same with "System Requirements" and "Add to Firewall list" ones) and, last but not least,
no custom code required to sucessfully compile that.
The compile error was because it cannot find the "getLngID" function, which won't come with the extracted script.
BTW,
the "innoUnp" (Command line app used by Universal Extractor for InnoSetup unpacking) site explains that it extrats a PARCIAL script - Only the basics.
There are a LOT of codig that won't be unpacked this way, so you need to add them by hand. And guess what? No "easy way" to do that, no matter where you find all thye codes, no matter how easy is the Inno's coding (Pascal, right?).
To edit the setup the way you want,
you must edit some code already avaliable. I've already gave a suggestion some posts ago, now it's up to you.