Please explain what you are referring to as far as “want to transition from M1XEP but still keep network adapter to C1M1” .
The C1M1 is not a DIY’er product and needs to be registered by a Licensed Security Professional or supporting Central Station with Telguard and then on ElkLink before the C1M1 will work. The M1 Gold will support either the C1M1 OR the M1XEP connected to the M1 onboard serial port but NOT both. Once the C1M1 is registered properly ElkLink stores the Central Station information. The C1M1 will check-in to ElkLink periodically to see if any Central Station information has changed.