Thanks for open the discussion.
Probably the easiest way for the developer is just copy the RUI file in the same folder as the .rhp, and Rhino is who take care about loading and version control of the RUI file. Possible workflow.
When Rhino loads the Plugin:
If the RUI is not loaded:
1) Copy the RUI file to any User folder (Roaming,...)
2) Add a tag of the plugin version in the RUI file.
3) Load the toolbar to Rhino.
If the RUI is loaded:
1) Check if the RUI files (User folder and Installation path) is the same.
2) If is not the same, do the previous steps.
If you have any question, please let me know.
Thanks and best regards,
Rafael del Molino
TDM Solutions SL