.....My question is, can I safely run a shorty pipe made for a zx10r on my 250r after I re jet it to accommodate the air flow/less back pressure?
The short answer is no. The pipe you want is designed for a 4 into 1 or bigger 2 into 1 exhaust with much higher output. The sound you will get is real raspy, crackly and hollow and not deep and rumbly as you expect. Some folks like the sound, but the performance of it falls short. Not the exhaust you want or need for the track.
The only Ninja 250 I know of personally, that runs straight pipes successfully also sets land speed records. https://lh5.googleusercontent.com/-S...jpg?imgmax=912
The Ninja 250 is a 4 stroke and needs a little restriction or baffling to work properly, even with proper jetting. To run a straight pipe on the Ninja 250 you really need a bit more modification than just jetting and a pipe. Intake filter changes are necessary as well if your bike is stock. You should include tuning on a dyno to get it dialed in correctly if you want to get the best performance.
Exhaust pipes from other bikes have been modded onto the Ninja 250, however the mufflers were included. The stock 08-10 head pipe ID is 1". The outlets are 1 1/2". The exhaust pipe you're looking to buy has a 2" O.D., so a mid pipe will be needed.
If this is your first bike, you may want to start with some simple tips
to help your bike's performance. Try not to get hung up on sound too much, it's not a real performance enhancer for most real racing applications.