I upgraded my Doubleshot a few years back using the instructions on this Candlepower thread; unfortunately it’s sufficiently old that the pictures no longer work.
The LEDs in the Doubleshot – and presumably then the Tripleshot as well – are a straight swap for Seoul P4s, although they are bare emitters rather than ones mounted on stars so the swap is a bit fiddlier but still fairly doable. The hardest bit is removing the screws that hold a plastic bit over the LEDs which are made of soft cheese and extremely difficult to get out intact; luckily you don’t really need all of them for it to still hold together (mine is missing two of six IIRC!).
My upgraded doubleshot isn’t a patch on a Magicshine on high or some other recent equivalent but it was a decent upgrade from what it used to be and well worth doing.
Looking on Dealextreme the P7s look very similar to P4s; I wonder whether they would fit? My doubleshot has been retired now, so maybe it’s worth an experiment… 🙂
Edit: The tesco torch I have is brighter but muuuuch narrower; the upgraded doubleshot is far better in terms of spread.