How can I force default text in a custom field is changed by a user before transitioning an issue?

[Miles Monty]

Hi everyone,

I have a custom field that gives people template text to prompt them to provide more information before transitioning an issue to QA. 

I'd like to use a validator or check somehow to make sure that people have actually changed the text, but the 'Field has been modified Validator' isn't working, I think because it already has default text in. 

Any suggestions for solutions? 

Thanks in advance,

Miles