Depends on the post, and the control. On a lot of machines with newer Fanuc controls, if the tool currently in the spindle is called with an M6, it just returns to home, calls all modal commands again, then continues along. For older controls you could add a logic check in the post that omits the M6 if current tool is same as tool being called.

finally im back reading through all the replys, thanks everyone. jp that was what im looking for to start(18000 wow my new machine goes to 10000, old one i dont run above 6000), and colin for what i want to advance to. Our shop is basically still running in caveman times. im trying to learn all these new toolpaths mastercam has(im still taking .05" depth of cuts), and surprisingly i know mastercam better than everyone in our company and i know nothing compared to people on this forum. matthew i downloaded HSMAdvisor thanks, have to figure it out at work. again, thanks everyone!