Which preparations will be needed before changing the Jira username?

[Jakob Nielsen]

Hi, 

As part of a merger, we will need to change the Jira username from email to an internal company ID.    

Scenario 1 works for us, and we have changed the usernames on a nonproduction environment. 

What could this change potentially break in Jira?

I assume references to usernames in queries, quickfilters, scripts etc. will all need to be changed, but what else could be affected? 

Since username and email are currently the same attribute, could potential issues be mitigated by referencing users by email instead of usernames? 

Thanks!