That's basically what I ended up doing last night. Your post, though, is still appreciated, since it's just as helpful in general even if I did it before reading it. (Only I mapped | to down-arrow+fn.)

In other news, I have something which may be insightful into the "error unable to load new keymap definition" error. Last night when I was editing and reediting my rx-51 file, it randomly decided to give me the error again. Between the last working setxkbmap command and the first non-working one, I had merely cd'ed to another folder in a seperate directory, sudo gainroot'ed, and exited (command "exit", not closed the window) in a seperate terminal window. I also turned off wifi and that's pretty much it. Naturally, I had to have opened vi to make the edits I was trying to setxkbmap for.

Rebooting (after changing the rx-51 file to the last working version again) fixed the issue. So now I think it's either some instability that is created by something I have installed, that surfaces through some combination of system events, uptime, or a mix of both.

- Edit (writing this stuff down so future readers looking to remap their keyboards have this available, and so I can remember to add it to the wiki page) -

My FreOffice still registers the fn+space as a space instead of tab. I think this is a purely FreOffice bug, but it may be linked to that hardware problem about some keys giving the output of themselves and the key next to them when shifted or fn'ed. The only thing that makes me doubt that it's purely FreOffice at fault is that when I have my upper arrow Fn'ed to give Tab, FreOffice gets it perfectly.