Fred, what will most probably happen is that the bolt lug will crack.  That happened (and continues to happen) to many Krags simply by overloading the powder pushing the 220 grain bullet. I did it to my Krag with 41.5 grains of 4350.  Someplace on this site is a link leading to Michael Petrov's experiments in blowing up a Krag.

That said, I have seen Krags converted to both .35 Winchester and .405 Winchester.  The magazine must be modified to take the slightly longer cartridge.

Ken Water's Pet Loads book has chapters on all 3 cartridges; .30/40 Krag, .35 Winchester and .358 Winchester. Walter's work is well worth reading, especially the part about asking too much of old rifles.