Basically, I think there should be a block that allows the sprite to have a pen that's coming from a sprite from a layer higher than its to overlay the sprite.
This block would allow the pen to go over
This block is for if you want to stop allowing the pen going over that specific sprite.
This is to check if the Pen is allowed to go over. Though this can be easily replicated with a variable.
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Maybe a non-scriptable icon like the draggable lock icon is better for Scratch's purpose.
However I don't feel this has the importance to make it through to a concrete feature.
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