i was on ebay and saw what was described as a polaris piston sleave. my question is could you change piston size just by replacing the sleave and a new piston?

 

you resleave the cylinder either after you have bored it out the maximum size or have scored the walls that the sleave can no longer be bored out.
generally you buy a sleave take it toa shop and they press the old one out and press the new one in then bored and hone it to the proper size

 

Yes....you have to take it to a machine shop though like eggenz7 wrote.