What do you mean by "User Story" field? Is it a custom field, or do you mean something like the Issue Type?
I assume by "lock" you mean "disallow changes" - there are ways to do that, but I'd need to know what the field actually is before I can start to describe what you'd need to do.
For JSM June Challenge #2, share how your non-technical teams like HR, legal, marketing, finance, and beyond started using Jira Service Management! Tell us: Did they ask to start using it or...
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