party SIREN and registered address SIRET should be immutable
In all countries, the unique company identifier is immutable. That is, once created, it cannot be changed.
A different company identifier means a different company (party).
In France, the SIREN is the unique company identifier, but it is not read-only (once set and validated). It should be. The SIRET on companies registered addresses are too.
When setting the unique company identifier, the validation process should contain minimally the steps to control the identifier value itself, uniqueness in the database as well as perhaps even create and/or validate the primary (company HQ) address fields (which could be left to the country's accounting plan modules to provide).
For example, in France and other european countries, the validation process could also automatically setup the VAT identifier with VIES validation included, as these steps are currently disassociated and somewhat dysfunctional though to be formally correct they need to be.
There is probably some more modeling that needs to be done to better support the company view of an address as opposed to the pure geographical aspect, given real estate changes hands over time as well a do the occupants in the case of a lease.