Alex, welcome to the Marlin forum. Boyd's makes some very nice laminated and walnut stocks to fit the X7 series of rifles. i am guessing that you are looking to add a detachable magazine to your rifle? well my guess is, yes it's probably possible, but would be a lot of work and more than likely need the services of a good gunsmith. another option would be to make a dropping floorplate assembly. would need a new triggerguard/bottom metal assembly, and opening up the bottom of the stock. i think going to a laminated or wood stock would be prefered over the factory synthetic for this type of project.
i restocked my XS7 in 7mm-08 with a Boyd's grey laminated stock, because i have intentions later on, of rebarreling the action with a heavy fluted stainless steel barrel. the laminated stock would be much easier to recontour for the larger diameter barrel than the factory synthetic one.