I don't hold with the purists who say you never alter a mil-surp, especially not when you're talking about the Mosin, of which there are upwards of 17 million in the world. We're not going to run out of them anytime soon, and even if we alter millions of them, millions will remain in their unaltered state.
These rifles can be made much more attractive with refinishing. I have two Mosins -- a full-length 91/30, and an M44. I just refinished the stock on the M44. I used some furniture stripper from Home Depot and it took the Soviet shellac right off. This left the naked birch, with very nice graining and some antique-looking blemishes and dings. I very lightly sanded the stock (there were no arsenal stamps on it), then applied one coat of Minwax "natural" stain, so as to give the birch a honey glow. Then I coated with five thin coats of clear satin Minwax Polycrylic. I wasn't going for cosmetic perfection at all. I just wanted the honesty of the wood to show through, with its graining and its blemishes, the very things that couldn't be seen under the original slathered-on Soviet shellac.
Above, the refinished M44 on the left used to have the same heavy red-brown shellac as the 91/30 on the right.