If you want to use interface ens1 and it has a hardware address of b8:ca:3a:64:da:c8 (on bridge br-ex) then try to have file ovn-chassis.yaml with the following contents:
I can confirm @pmatulis’s suggested approach will work.
Juju charm configuration affects all units of a named application.
If you have 6 machines with deviating configuration your choices are to either list the MAC addresses of the interfaces as @pmatulis suggested above, or to add a second set of named applications for nova-compute and ovn-chassis and fit them with a different configuration.
Thanks with your replays I understand how that the configuration is global .
At the end what I did was to change the name of the interface in MAAS before deploying the unit.