Add Custom Fields to Comment Screen

How difficult is it to add a custom field to the comment/reply/resolve
screen? On the create screen, all of my custom fileds for a given queue
appear, but subsequent changes or comments require the user to access the
jumbo tab to have access to the custom fields.

I’d like to select one of the custom fields for a queue and populate the
comment/reply/resolve screen with it. The other fields could also appear,
but I really only want the one.

Is that something that I have to change in the GUI or edit the file
directly? How can I do it?

Sorry if the question has already been asked. I couldn’t find the answer
in my searches…