How to merge multiple custom field context for a field

Hi I was trying to merge the multiple custom field context for a field A. Is there any easy way to do this. Field A is a single select and having 3 context for different projects, now we want to make that into a single context with all projects and values. How we can merge this using script? Also we have 1000+ number of already created issues so how we can update that issues. Any scripts to achieve this is very helpful?

Is not going to be an easy script.

At first, you will need to obtain the 3 contexts of Field A using com.atlassian.jira.issue.customfields.manager.OptionsManager interface.

Once you have that you can use the same interface to create the options in the new context, that you can create manually.

When you create the new options, you should store the relation between the old Option and the new Option, and with that relation update all the issues.

I hope this can guide you. Thanks, Ivan.