I have a "Checkboxes" type custom field. I want to add "Uncheck-All" to the options that deselect all the selected ones. Any help would be highly appreciated.
You can use ScriptRunner behaviours or ScriptRunner listener. Both option requires programming skills. Another option is Automation for Jira, it works simillary tu ScriptRunner listener. Let me know which of those add-ons you have and I can help you resolve problem.
You might be able to do something like that with Automation For Jira. You could have a rule that checks for when the field is updated and if the Uncheck-All option is selected, then clear the field. This would not happen real time but when the user saved the value for the field. In other words, as soon as they click the option for Uncheck-All, it would not immediately clear the field.