Religious Conversion - what will happen

[Iriath Zhul]

So if my ruler converts to a faith (considering Catholicism, as Hungary from Taltoism), what is likely to happen? Will there be sudden populist revolts? Will my vassals convert their own territory if they happen to convert alongside me?

[CrUsHeR]

You can see exactly which vassals will convert, and there is a breakdown of the factors influencing the conversion.

If a ruler adopts a faith, their capital county always switches along with them. Peripheral counties have to be manually converted, unless they are held by sub-vassals, then the procedure is up to them.

Note that you can always revoke barony-tier vassals (city, castle, temple) without tyranny and 100% acceptance.

Generally a zealous vassal is more inclined to send his priest to convert his counties. IIRC there is a hidden stat called "zeal" like in Ck2 which influences further decisions by an AI ruler.

[T-Murdah]

Manually asking vassals to convert (those that didn't during relgion reform) usually works if the opinion is high. A bit of micro management if your realm is huge but really speeds up the process.