If you are looking for a more secure way to log in, set up a username and password for the m1XEP. Serial port is secure due to the need for hardware access. Some RS232 commands will require a user code.
Are you trying to crack the RP code for an elk M1 that you did not buy yourself? As far as I know the APIs used by ElkRP are not publicly available, but if you are handy you can probably sniff the packets and see what it is sending if it is not encrypted. Alternatively give ELK a call and they can advise you on how to reset or have you send the panel to them. I don't believe there is a way to reset the RP code, but there is a way to reset the installer code if basic config is all you need.