anyone ever done this? Tim
Tim, Three times so-far. With care you can strip the glass and not lose too much foam. don’t expect to net the same type of board out of this process as you start with, it’s very hard to strip the glass and not loose tails/wings/nose/etc details. I sanded through near the rail and peeled two of the three. Third was so delamed that I just cut the skin at an old ding and started pulling off the glass however it ripped. Probably a much better method is to set a shallow cut on a router with a straight bit - just enough to cut through the glass, and run that around and pull off the glass. Still, the fine bits will be hard not to destroy. If you want to use the width of the board, or close to it, be very careful on stripping the rails. It’s easy to take out a chunk if you horse it too much. the deck will be soft on the new shape = extra layer of cloth. good luck.
I suspect that many people had their introductions to shaping this way. Be prepared to pull out a full bag of tricks on this one (extra layers of glass, repairing holes with spackle, elmer’s glue with sugar, cut-out foam patches…etc). it’s a great way to gain experience without too much at stake. I ended up with a really soft deck, so I lammed (on Herb’s suggestion) two deck layers, then another deck layer on top of this. The board was ugly as hell, but it floated. Good luck!
I’ve done it. make some cuts and pull it off in sections. I found a thin piece of sheet metal helps take it off pretty clean. just slide it under the glass to break the bond to the foam, nothing too big because it can bend and dig into the foam. if you have a sander you can grind away most of the glass too.
Made this out of a longboard i found snapped in half at a local beach. Rides like a champ. 
i was watching a …lost video a few years back called 5-5 x 191/4. i was looking at the outline of one of the “fish” shapes they were riding and thought, "hey, i could get that out of that old 6-10 in the garage!! pulled it out, layed the template on it, and cut it out. stripped the glass after! pulled the finbox, put some foam in its place and the board ripped, only 1 foot shorter and a tad bit thinner than the original. still have it.