Ranking custom field in Epic

[Vi Phung]

Hello there, 

We have a ranking custom field in all Epics. My question is how could we get the ranking to adjust accordingly? 

For example, Epic A is ranked #1 and Epic B is ranked #2. When I added Epic 3 and ranked it #1, other Epic will go down by 1 (Epic A = #2, Epic B = #3)

Is this possible? Can I write some code using REST API? Looking for advises!

Thank you for your help!

[Nic Brough -Adaptavist-]

Is this your own numeric ranking field, or are you using a rank field from Jira Software (which already does this, albeit slightly differently)

[Vi Phung]

It is like below. It is an option that the manager can choose. However, we are stuck with the dilemma that the priority (rank) does not adjust accordingly. For example, if I assign Epic A to be Priority 1. Later, I want to assign Epic B to be Priority 1, I would have to move Epic A down to Priority 2 manually. I'm not sure if there's another better way to rank Epics. 

Thank you for your help.

[Vi Phung]

the reason why I'm trying to do this so I could workaround the rank in Portfolio. I understand Portfolio is a live app. But we don't want epic rank to move whenever a user story moves. So with this ranking in epic, we hope we could avoid the "live" ranking in Portfolio.