If a tiled background has 'solid' can I 'non-solid' part

So I have a 'ground' tiled background and a wall tiledbg. The wall is solid and it lines the ground tiledbg.

Can I ignore a section of the wall by putting a ground tiledbg on top of it?

I would guess no, you can't make an object that is solid non-solid by adding a non-solid object ontop of it. However you can have tiles in your non-solid background look exactly the same as tiles in your solid background, then remove them from your solid background when you desire to turn it non-solid.