So my example would compare the buildings with heros. Each hero has the option to lock them when you select them in your hero list, which removes them as an option when trying to level other heroes, as they are marked as favorite.
Keeping this in mind each building has a question mark button. If you clicked it a check box could come up under the description to lock the advance building as a favorite and remove the convert button, which is conveniently located next to the upgrade button. You could simply uncheck the box and fonver back if youd like.
I dont like seeing this opition as I’ve converted buildings I dont plan on converting back to. More of a cosmetic update as we are going to get more advance buildings.