The hash check is performed on the files on your hdd, nothing stops anyone really dedicated from changing them after being placed in the ram (which should be even more easier since everyone disables "load textures on demand" - and yeah, ofc one could easily randomize the position of those files in the ram by using features in win 7/win 8)
But I guess whitelisting mods will be the best solution - for melee. shit wont happen with crpg, after all the modability of warband is what got us crpg in the first place.