Hi @Daniel_Porter ,
The ledgerId is read from config and used as part of the initialization of the participant node when it starts (the two ways you mention are in fact the same one: the config populates the value in CantonLedgerApiServerWrapper.Config.ledgerId). Currently, there is no way to change the value once the participant is running.
Maybe what you could do is to pass the config value via the command line?
Cheers,
Raf