Resize selection/layer/object, but keep number of pixels?
Let's say I've got a red rectangle, 200x300px.
I copy the lower half of it (200x150px), paste that as a new layer, and make it black...

Now I want to be able to transform that black layer, but keep the exact number of pixels.
In other words, I want to literally change the shape, but not scale it up or down.
For example: if I tried to make it higher, I'd want the width to automatically decrease.
Is this at all possible?
