I think if you are using something intermediate modulus, non-post-cured like west 105, system 3 or
Resin Research, you can probably do it. Would be fun to try.
How good a shape result and how much strength would be left, harder to guess.
I would try first, find out what range of temps is between post curing and decomposition of the core and the resin matrix. Then see how the core and resin thermal expansion coefficients match up within that range. If they are close, good- maybe you can just heat the whole board up and mash it into a rocker table. If the expansion numbers are "sort of" close, you can probably get away with it, since it is a thin core. On the other hand it could
If your numbers don't match well, or it just doesn't work, then next idea I would try depends on how you built it.
If you forced the rocker in on a table during layup, the fibers will be slightly prestressed, so you might be able to gently grind off part or all of the deck lamination near the tips and have the tips spring back naturally to the base rocker line. A little heat aplied to the deck could help it along. Hopefully if you have the base rocker of the board still on a table you can then relaminate the tips on the deck side and lock it all in on the table. Would be cool to not have to redo the edges and bottom glass...
If this didn't work and I had the time, or if rocker and flip was carved/shaped in rather than forced in, I guess I would start grinding on the bottom as well until it got floppy enough, then reglass the tips at top and bottom. No idea if your results would be strong and pleasing to you, depends on a lot I guess. If you do reglass, keep a good long feather edge on the layers. I think the standard for scarfing in glass is like 20 or 30:1. This might all get to be too much trouble though.
But if the board rides "ok" just not your style, maybe you could can sell it for enough to buy materials and make another one in only a little more effort. But I think the first step is worth trying for sure.
Good luck, caveat this advice is partly hypothetical, haven't built that
many boards... Did have one lose rocker in a hot car though