Yes, a Pokemon can use as many Poke-powers as it likes during a turn- however, if a Powers that state they can only be used once during a turn can only be used once during a turn (i.e. you can use both Conversion and Decode in a turn, but you can't use Conversion or Decode twice that same turn).
Of course, if a power says that it can be used as often as you like (such as Magnezone Lv. X's Electric Trans), you can use it as often as you please.