You can modify field descriptions and red warning messages on-the-fly, possibly to reflect changes in requiredness. Example, on changing the priority to Blocker (or Highest in newer JIRA versions), the Description help text changes:

high pri

To do this you put a validator on for example, "Priority", with the following code:

def formField = getFieldById(getFieldChanged())
def descField = getFieldById("description")

def priority = formField.getValue()
if (priority == "1") { // Blocker or "Highest", priority
    descField.setHelpText("Please explain why priority is Blocker.")
else {

For how-to questions please ask on Atlassian Answers where there is a very active community. Adaptavist staff are also likely to respond there.

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