For me, exporting 20-50 costumes is a pain, especially since it takes up to much room on my computer that doesn't have a lot of space. I have to end up deleting them, and not having them when i need them.
My suggestion is that when you export a sprite, all the costumes should be exported, and any unwanted costumes can be deleted at will.
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You can already do that. Just make all of your costumes, and right click the sprite's icon in the sprite pane. Then click "export this sprite." All of your costumes (and scripts) will be exported to a single file. When you want to use it again, go to the sprite pane and click "choose new sprite from file," and open your saved sprite.
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