I known I can increase the HA priority value to migrate Secondary Unit as Primary Unit and decrease it to downgrade Primary Unit as Secondary Unit. I'd like to know, is it different between the two methods?
1. increase the priority on secondary unit to Primary and 2. decrease the priority on primary unit to secondary.
If you're using override, sounds like you are, and you want to do the failover semi-permanently, only other parameter you can tweak is the number of failed monitored interfaces. As in the flow chart below: