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.

@Rednax he's not talking about that, he's just talking about the default tick procedure

It is possible, and actually very simple. You can make a procedure that has a global "On World Tick Update" trigger. In there, you use an if block to test for if the block at the current position is a vanilla block. Then, inside, you execute whatever you want.

Update: It is not possible with that method. What exactly do you want it for?

I was doing something totally different from what this was asking, lol. It is really easy, all you have to do is check on global trigger "On block placed", then wait a few ticks on sever side (usually 3 ticks) then place block on the position. If you want it to not immediately replace the block, you can either add more time to the wait a few ticks on sever side, or set the position of that block into 3 different number variables, then set a logic global variable to true, then on another procedure on "On world active tick" check if that logic variable is true, then add to another number variable for counting ticks, then after it counted to the amount you want, then replace block at your saved location variables until it's the custom block. This will only work on 1 block at a time, but it'll work. If you want other was of achieving this, I have a million other ways, but they really only work on one block at a time.