Can I change after which level the text episode endigs show with DEHACKED in Doom2?

As tittle says, I know I can change the text content but I want to know if I can change their placement outside zdoom.

If you're bothering with compatability with chocolate or vanilla doom, then you can't, sadly. If it's specifically an ending you're making that's before the 30th map, you could make an ending map to signify that you've reached the end and house the text there.

However, a special version of PRBoom+(And also GZDoom) supports something called UMAPINFO, which allows you to put text screens and/or make the game end after any map, among other things.

This is your only option if you want to have a text screen ending before or after MAP30 and have it be playable in something that's close to vanilla.

@Alper002 thanks! I meant those text screens like the ones after map06, map11.. etc, so with UMAPINFO at least in prboom and zdoom I can do it, do you know if that UMAPINFO will conflict with a ZMAPINFO I made for zdoom users?

If you make a ZMAPINFO, then GZDoom should completely ignore any other MAPINFO variant, so there should be no conflicts with UMAPINFO then.