What happens when I remove a key level my trades already use?

It is archived, not deleted. Every trade that carries the level keeps it; the level just stops appearing in the pickers so you cannot tag new trades with it. A level nothing uses is deleted outright.

The × on a level row checks how many trades use that level before it does anything, and the answer decides what you are offered.

If nothing uses it, you get a plain delete: "Delete 'pdVAH'? No trades use it, so nothing is lost."

If trades do use it, you get an archive instead, counting them: "'pdVAH' is used by 14 trades. Those trades KEEP it — archiving only removes it from the pickers, so you can't tag new trades with it."

Removing a level only ever changes what you can log next. It never reaches back into trades you have already tagged. That matters more than it sounds: an entry level is one of the few pieces of context that explains why you took a trade, and losing it across a year of history to tidy up a dropdown would be a bad trade to make.

Archived levels can be restored. An archived row stays in the list marked Archived, and clicking that badge puts it back in the pickers.