Same bike as me more or less. What length fork do you run. Just think about it like this. If you drop your rear wheel size down you change the height of the bb (lowering it) and make yourself sit even further back over the rear dropout then before (on that bike you don't sit over the bb but more over the rear wheel like on mine). With a 24" rear on the back that changes even more. This stabalizes your ride (close to the ground) but also puts you so far back you will be able to wheelie very easily (not a good thing going up hill).

You get the same affect by adding a longer fork HOWEVER with the longer fork you increase the bb height. Either way your geometry changes but on that bike I wouldn't go with a 24" wheel. The geomtry with the jrt2 would be weird...(ok ugly...sorry)