Thanks for flagging me, @abctax55!

@qwertyui You can override the due date so that the client letter, which is really just basic filing instructions, will show the proper due date instead of the date to which P&I are calculated.  But there's no way to change it to something like ASAP and provide a more elaborate explanation that the P&I has been calculated to a certain date, etc.

The override can be found under General > Letter, beneath the Client Letter section, on the line for Due date of return [Override].

If you would like to further customize the filing instructions, using a PDF editor will not get you a lot of milage because of way texts are formatted.  You'd be better off creating one with Word.