Here is another clue, all the information for each and every loco is stored and controlled by the LM's, not the HC. All the HC does is access the network of stored information on all LM's at any given point in time as well as facilitate the loading of an LM with all of its relevant data before its first use in a loco.
Once an LM has been initialise it will access the network and Tx it's stored data onto the network. Ring clearly state that each LM is its own Transmitter, so it's the LM's doing all the heavy lifting, not the HC.
Given that, why would you not have a LM able to use a Repeater to talk to another LM since by RailPro's very own definition, it's all about radio networking using one code that is small light and fast.
As to how can a LM access a password repeater, I say the same way as it access a passworded LM. Passwords are to control HC access, not an LM's ability to do so.
Remember an HC is NOT like a server.
That's how I understand all this to work, could be wrong though. 😀.