I'd like to modify my personal mod so that only 4 techs found religions.

Using the 'Choose Religions' option should then, in theory, have different combos of religions every game.

However, setting the TechPrereq to NONE causes them to be founded on turn 3 (as if the tech were discovered).

How do essentially set the tech to 'NONE'?

Or would it be easier to have a 'hidden tech' that can't be researched?

if you just wanted to have 4 religions, it would be as easy as deleting one from the xml file and its dependencies.

however, since you want 5 different ones in total but only 4 available per game, and choose freely out of those 5, to me the simplest way is to create a dummy tech which founds the 5th religion. you can then disallow researching the tech with bDisable.

that should do the trick. to create a dummy tech, just copy paste a basic one (eg. fishing) and make the obvious changes to type, flavor etc. so that it's a useless tech.

That's how I've handled it. TECH_RELIGION added!