Sure I could add those 20 extra lines to my otherwise small 100 line script.
But there is no need to as long the user can read what the hell he is installing. It shouldn't be my job making sure he reads it.
"You're trying to fight a user reading comprehension issue by requiring extra code. " - What this topic is pretty much about. Granted we need a L4D2 drop down option (why is it again we don't have it?).
#5 (plugins changing cvars)
There is no elegant way to do this. It will just cause more troubles and add a lot of unnecessary code.