At times, when baking a pie, I have wanted to put a disc of almond paste between the crust and the filling, only to discover upon opening the tube that the contents are old enough to have dried out. There’s no rancidity - it’s just that I tend to buy things with the intention of using them promptly and next thing you know, a couple of years have passed.
Even grating the cylinder is impossible. Microwaving melts the exterior while the interior is still hard and dry. Does anyone’s sleeve contain a magical fix?
You may not be able to save it. Any “trick” to save brown sugar should help (microwaving, steaming, putting in a bag with white bread/Apple, etc). But I find that even brown sugar can get too hard and crystallized to be saved. Good luck!
I would try cutting it into chunks and putting it into either a stand mixer with the paddle or a food processor and making it small then adding a bit of warm water to soften. It may break and turn into a mess though, overworking marzipan can be risky.
How about buying the marzipan that comes in a can? (Solo brand). It should stay pretty usable in the unopened can for at least a year or two. And if you use some, but not all, of the can, you can store the rest in a small plastic container in the fridge. I’ve done that many a time, and the leftover amount lasts a good while.
or perhaps you do