Persistent means that the data persists from one session to the next.
We save persistent data in attribute dictionaries which changes the model, yes.
There is no way to write persistent data (ie save it,) without also saving the file.
Your code has a comment that mentions the UUID is for the session. Is this correct?
If so, then Entity#entityID should be used during a session if the id does not need to be persistent.
Since you cannot save it to a attribute dictionary (which would change the model,) you’ll have to save it to a collection as extension data. Ie, a Hash or Array of data records.
The records could be subhashes, Structs or OpenStructs.
See the Ruby Core docs or Ruby books on these classes.
Also, you are free to save extra model data as files.