I have a custom field that has context enabled and limited to certain projects. If I change it to allow the field to be part of all projects is there any impact to the existing projects that are currently using the field? I don't think there should be as I am opening up the field to more projects, but this is Jira Cloud, so sometimes things don't always work the way we would expect. Your help is appreciated. Thanks!
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Nope, you're safe, a change from a local context to a global one will do nothing to your existing data or usage.
In the other direction, you might lose data if you tell Jira you want to, but local to global won't risk that.