Describe the feature

Maybe you could add a frame which is stackable in the same way snow-layers are. This would be possible in all 4 directions, essentially allowing for vertical slabs with custom thickness.
The BlockCarpentry Mod already has such a feature, maybe you could take a look at the way they do it if I didn't explain it that well.

actually, that pretty much serves the purpose, thanks! However, is there any way to quickly reproduce certain modifications of these blocks? For example if I wanted to create a wall using a 4-pixel wide collapsible cube, would it be possible to get that without having to collapse each cube manually?

Yes, that is indeed possible: collapse one block to the desired thickness, right-click it with a Framed Blueprint while crouching to copy it (including the its camo) and then use the blueprint to place the copies. The only limitation of this is that you can't turn the copies, they will all point in the same direction as the original block.

The Framed Collapsible Cube should do what you want, it can be deformed by in any of the 6 directions (though only one at a time) and allows different deformations per corner. To move a corner inwards, hit it with a Framed Hammer, to move it outwards, hit it with a Framed Hammer while crouching.

If that doesn't allow you to do what you are looking for, then you'll need to get into more details.