You can also change the name of the savegame folder!
1. open the EBOOT.PBP with a Hexeditor and goto offset 00050400h
2. Here you see SCUS94476 or something like this.
3. Change this to whatever you like and save and copy the new EBOOT.PBP to your PSP...
4. Now the savegame folder will use the new name entered at 00050400h and will not overwrite anymore...
It works for me!