Maybe have a short cooldown replacing others' pixels when you have stacked them? Or removing the 30 second longer cooldown for replacing your own?
Edit: Two more suggestions: Ability to place Virgin pixels for your own work if you made a mistake and the undo button has faded/you have already placed another pixel and an Undo key (like "O" or something) to undo after the bar fades.
FWIW as a sidenote I just wanted to point out that it seems the system tracked pixel 'virginity' based simply on whether they'd been touched at all before, including corrections; rather, it was background pixels that didn't charge the extra cooldown, from what I could tell.
Sorry for the silly nitpicking about wording, though given that the Canvas treated these two properties separately I wonder if this might be useful information for whoever runs this next time.