Hi Lorne,
At the moment, there is no tool that will let you extract games from another firmware seperately and import it back into another firmware unfortunately.
In terms of 'reskinning' or retheming your player, there is a Knowledge Base on how to do this:
How to: Modify your firmware using s1res tool located
here. This guide will help you reskin your player. It's best that you do this yourself rather than someone else to do it as you know for sure what you've done. There's no guarantee that someone else might stuff it up for you too.
Re: FM transmitter.
Does your transmitter transmit any other radio frequencies though? Mine has four to choose from so I can change it instead if it clashes with another radio station. If not, then you'll have to probably get another FM transmitter instead. There is no setting on your MPx player itself that lets you change any of the settings for FM transmitting, it's all controlled in the FM transmitter.