I've never used "Copy" (currently F5), as I just drag and drop my files between local and remote machines. Thus, I want to change "Refresh" to F5 because I use it so frequently.
The same is true for "Move" (currently F6), as I use "Duplicate" much more often and want to change it to F6.
I wouldn't burden such a change to the core, therefore allowing this type of hotkey customization should be built into the prefs. :)