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I have no clue.  But whatever it is, it'll take longer than swapping two wires on the motor.

When switching from tractor to pusher:
* Switching any two motor wires will reverse the motor rotation.  Most ESC's can also be programmed to accomplish this - do what is easiest.

* Not all of the the pushers are direct mirror images of the tractors - you may have to tweak the RPM up or down a little.  I always suggest erring to the slow side then sneaking up on your setting.  

* Trimming: the differences are pretty subtle, they will not make your airplane crash.  However:

*With a pusher you will probably note more yaw and a increase in line tension.  You can probably move the leadouts forward a little.  If you can adjust your rudder offset you can likely take it to NONE.  Both of those will reduce the yaw and drag, and in effect speed-up the airplane, so in extreme cases you may be able to go back and lower your RPM a little.

* Sometimes the opposite prop rotation will also expose behaviors that look like a wing warp - a tab or flap tweak might come into play.  For me this is easiest to see in the overhead eight - where differences in inside and outside loop line tension and rolling are easiest to see.