Howdee,

AFAIK diamond coat is a clear coat.

I'm interested that yours also has had mylar put down.  In theory, your insert decals should have been screen printed on under the clear.  Certainly mylar removal (which has gone down over clear) should be a lot easier as long as its done correctly.

If its an aftermarket decal kit, then there is a risk that they may come up.  Having said that, when I removed the mylar after my 1st decal kit, only 2 lifted.

If you can remove the mylar with the diamond coat in tact, the playfield should come up like new!