Just ran into a situation where someone tried to remove inserts from a playfield, and cracked over half of them. Most of the time, there isn't any reason to have to remove an insert. Heat or not, your more than likely going to shatter, or put hairline cracks in the insert and ruin it. If it's raised. Use a clamp and blocks of wood and press it back down. But don't remove them, just because you want to reglue each one. Your just going to trash your field and many inserts are impossible to get. If it's loose and practically falling out, then yes, push it out with your finger and reglue it in. If you have to use a hammer to get it out. leave it alone.
Just trying to save a lot of newer people from ruining their games.