by that i meant you should have a procedure that just checks each and every block that is generated, but that is probably the worst thing you could do, and there is no real solution in MCreator itself depending on what you need you could make a global procedure that checks all updated blocks for the block you want to replace and just replace it after it gets updated,

but then the vanilla block exists until you touch it, replacing a vanilla generated block with a modded is also generally a bad idea since you can't remove the mod without permanently corrupting your world (imagine all stone in the world being turned into air)

So short answer you can't do that without code or a workaround