Player on tile changes tile appearence

[Tosuxo]

For example, in my game Monster Trainer, I want it so that you can like, walk into some hugely tall grass and when you're on the tile, it changes it to a different tile, so it looks like you're making it move.

I'm not sure where to start, make it a new layer maybe? I really don't know. And I suck at blt lol.

If anyone can give me some advice it would be greatly appreciated.

Thanks