Adding a default value to a comments field

Hi all,

I'm curious to know if it's possible to set a default value in a comments field on a transition screen? 

I have a need from a customer to add a custom field checklist to the body of the comments field, my first thought was to use something similar to that of the default value for the description field. But I ran into the issue that I could not identify the comments field at all, so the script would not populate any info. 

Has anyone attempted this or has any experience with scripting this out. I'm trying to use a behaviours in script runner to execute this. 

Any help would be great!!

Thanks,

Norm