Adding a new status to JIRA releases (say Planning for e.g.)

[Mukund Iyer Rajamony]

Releases are currently in 3 statuses(statii?) -> Not Released, Released and Archived.

I see a reason for a release to be in Planning too. Having releases in planning helps further extract data and process for business accordingly.

Can the JIRA instance be customized to contain a new status called "Planning"

[Mukund Iyer Rajamony]

Well in this case, I'd like to make a case to atlassian to add a planning status to the releases. Or allow customizing the status.

[Pankaj Udasin]

I agree with you @Mukund Iyer Rajamony 
A custom workflow will be really helpful as in my org Program Managers need to track the end to end release cycle like Dev Complete, QA Complete, Hand-off to SRE, Staging Deployment & Deployment on all Production Platforms (GA)

[Pete Singleton]

No, unfortunately there is no way to add your own release statuses, although I agree this would be a very useful addition.

I came across this plugin a while ago which may help you: Release Board for Jira