how do i make vanilla blocks turn into custom blocks on tick (procedure)

This is not really possible

How it is not possible Klemen?? Just say On tick if block is that block than replace it with this block; roll random number if number is equal.
Mostly use flow logic math stuff in find replace block get block set block remove block stuff. I didnt try it.

yuno44907 you can't use on tick procedure for vanilla blocks

banarang_mods I am pretty sure it's impossible, but I'm a pretty bad modder with a lot of things. I think you can change a custom block into a vanilla one, and a custom one into a different custom one, but I don't think editing vanilla blocks' code is really possible without "brute force" modding as I like to call it - straight up going into Minecraft's files and messing around.