In 3.5 it specifically states you must use a command word to activate a flaming/shocking/etc weapon (which means blow a standard action to do this). The idea is that it seems like once you command it to do something else, it shuts off the original command. But it still seems open for speculation since it doesnt say anywhere Ive found "you cannot have multiple energy enhancements active at the same time" or such. Just make sure the PC activates them one at a time, good to go (although flaming/freezing weapon seems weird).
Technik