Unsealing heat-sealed stereo slides

Forgive me if this has been addressed elsewhere--several hours of searching these forums doesn't seem to have unearthed any answers.

I have a large number of stereo slides (Kodak Stereo Camera) taken and processed in the second half of the 1990s, when mounting quality was rapidly going downhill. Quite a few of these slides are either reversed or badly aligned, and I'm now going through them and marking those that need remounting. The trouble is, they're in heat-sealed cardboard mounts and I have no idea how to safely unseal them. I already have boxes of heat-seal mounts and a light box/cutter ready to go once I can extricate them, but the question is how to do it without destroying the film?

Any help is appreciated.

Thanks,
Lamont