Problem with the freeze method is yes, the glue no longer adheres... to the MYLAR. The glue will still be firmly adhered to the playfield and will need to be removed by soaking it with naphtha or Goo Gone and gently and PATIENTLY rubbing it off.

How much mylar are we talking here? Is the entire playfield mylared? If so, you're honestly looking at about 6-8 hours of hard work... and I'd recommend a complete playfield tear down if you're going to go that far.

If the mylar is in good shape and isn't bubbling, I would just take an exacto knife, cut off the excess flap, and clean up whatever glue is underneath.

If you really don't want to remove all the mylar...

To get in there with an exacto you're going to have to remove some parts.

For the top pic there is two things you can try. Heat that area with a hair dryer to soften the glue and try to stick it back down. If it just won't stick or hold very well, I would slice that "buckle" right down the middle, take a hair dryer, heat it back up a bit, then press it down.

For areas like the second pic, just cut off the excess that is sticking up and take a little naphtha and attack any sticky glue residue that may be left behind.