OK, feedback from my graybeard friend that's been winding transformers for decades.
Getting them apart.
Knife around the laminations one at a time to break the shellac and loosen them.
Extract tough laminations with carpenters pincers using the mechanical levering advantage they offer.
Reassembly.
You will likely not get all laminations back. As they are each sealed to isolate eddy currents cleaning them of shellac can compromise lamination insulation that minimises eddy currents. Not recommended.
A single missing lamination is unlikely to affect the ordinary transformer unduly that it shouldn't work as intended however they can run a little warmer.
To source replacement laminations exact internal measurements must be known, the width and length of the middle leg of the E lam are what the industry needs for suitable replacement laminations and best practice is to replace the complete stack for which the stack thickness needs also be known.
I now have some NZ contacts for these sorts of transformer parts but supply is normally only in bulk whereas for just a lam or 2 or a single stack my friend has offered his services if needed.
He's in Taupaki not far from me and I can arrange a hookup if required.