Paste a Sprite on another Sprite

Hi @jens! It's a very good feature that opens way to many new ideas! But it is somewhat restricted by two things:

  1. pasting cannot change the size of the sprite being printed on. And it's ok.
  2. pasting do not change transparent pixels parts of the sprite being printed on. And this restriction is quite disappointing. It would be great two have the ability to fill transparent parts of the sprite with pasting another sprite onto them WITHIN initial sprite borders! Or maybe it can be a setting of the "paste on" block: affect transparent pixels or don't affect. Is it possible to add this feature?
    Now I'm forced to edit directly "pixels of costume" list, and it is sooooo slooooow when you need to alter a lot of pixels.

Pavel B.