@UncleChuckle /tmp on Recalbox uses a ramdisk so its contents get lost when the power is turned off.
I think the best approach would be to write simple scripts to save/restore the file(s) you want to keep to/from a location that is permanent e.g. /recalbox/share/. Use the Recalbox event system to trigger that script.
And /recalbox/share/userscripts/amiberry[start].sh:#!/bin/sh cp /recalbox/share/CONFIG_FILE_TO_KEEP /tmp/CONFIG_FILE_TO_KEEP