You should be able to use a current developer license for modifying existing forms. If you need to add objects to the customer's license then I don't think they do that for unsupported versions.
Sorry, I meant to write "they want some format changes to their reports" instead of forms. Hopefully this will not be a problem - I don't have access to the db to check at the moment - was just doing some research for my employer...
Answers
RIS Plus, LLC
MVP - Business Apps
If you're trying to modify add-on objects it may be a problem is the add-on company does not allow other partners to gain access to their objects.
AP Commerce, Inc. = where I work
Getting Started with Dynamics NAV 2013 Application Development = my book
Implementing Microsoft Dynamics NAV - 3rd Edition = my 2nd book
RIS Plus, LLC
MVP - Business Apps
That's just what I needed to know - thanks! \:D/