You asked:
>>When I need to overwrite them, how do I save them first so I can "reload" then sometime later if I need them?<<
The easiest way would be to transfer the data (of the individual patch or performance) to the onboard sequencer, then save that data as a "song" (.svq file) and calling the song whatever the patch or performance is called. Later you can load the songfile for that patch or performance into your sequencer, play the sequence (which will load the sysex), and have your patch or performance back again. You can save an infinite number or patches or performances "off site," so to speak, as song files. The songs actually contain only the sysex for the patch or performance, not any notes for a real song.
-> Utility -> Transmitting sound settings-- 4 Data Transfer
Source will be either patch or performance TEMP. If you choose User, when you reload the data it will overwrite user memory; if you choose Temp, it will load into Temp. Destination will be "to Seq". Then name the song and save it as Song Only.