From the 4x5 film guide pdf (paraphrased):

"Don’t use fixers and hardeners

Polaroid doesn't recommend hardeners or fixers as it may damage the emulsion"

But from the 55 data sheet:

"To prevent scratches:
Negative scratch resistance can be improved by treating the
processed negative (after clearing in water and sodium sulfite)
in a solution of Kodak Rapid Fix with Hardener (parts A & B)
for two minutes. This solution should be made up and used in
accordance with Kodak’s recommended mix procedures,
chemical caution statements, wash times and temperatures."

In practice is it safe to fix and harden? Is it necessary?

I have 30 sheets I'm going to try out soon.

Thanks,
Greg

I can't really say. I have some 55P/N that was DOA and I exposed and processed it as if it were Royal pan, with a fix and a hardener without a problem, but then I didn't process it with the pod chemicals.

Two minutes in a hardening fixer should not hurt it. As stated, though, the pupose is really only to harden the emulsion and make it more resistant to scratches. Not a mandatory procedure by any means. If you get some type 55 P/N with dried out chemical pods, you can develop the negative normally. The film is Panatomic X.

No need to fix or harden, just clear it and have fun. I use tons of the stuff.