I'm sure someone will pipe in that knows more about this than me, but I'll give you my $0.02.
I put my pool in about 2.5 years ago. I had the same idea as you about changing jets whenever I wanted. I found that they don't really work like that - at least the Waterway jets which are by far the most common. You would think that the installation of the jet would be fairly simple, but I was amazed at how needlessly (to me) complex they made it. There was an initial sleeve piece that had to be carefully measured. The jet then snaps onto it. But those snaps are just little plastic tabs. Repeatedly snapping them in place and removing them would eventually cause them to weaken, and the force of the spa pump would eject them out of the sleeve. In fact with my 2.5hp spa pump (nice massage) it was already happening on the initial install - I ended up gluing a couple of them in.
Maybe there is a different manufacturer and a better way to have interchangeable jets, but I didn't find it. Perhaps we should start a company? ;-)
