If your HP41CL seems to lose the configuration after a low battery sign, or a change of batteries, and you are fearing to go through the whole installation procedure, do not fear! You don't need to do that. If you have assigned some keys using functions from a plugged in port, and you see XROM xx, do not worry: the memory loss has not been so big or so long as to lose the keys assignments, and therefore most likely the whole setting can be reinstated.
You just need to reenable the memory management: XEQ MMUEN. This will make the calculator again aware of the whole memory area. You can now use re-assigned keys and see that they keep the right function name on it.
This method does not work when you receive the dreaded "MEMORY LOST" message (below that of the HP41CL when it was born!)