The designer has three different ways of saving your layout changes.
Save Custom Layout in NAV
You can use this option if you launched the designer when running a custom layout. This will only save the layout to the NAV database for the current report. None of the dataitems or the report code will be affected. Even though you cannot modify the dataitems, you can still add fields to your report. This is possible because your ForNAV report has access to all the fields on the referenced tables.
Save Object in NAV
When you save your report object in NAV, it will be imported into NAV as a text object. The process happens automatically behind the scenes when you choose this save option. However, you need to have a developer license. Otherwise, the finsql client is not allowed to import the text object. The designer will test if this is allowed when you open the report. It will test if you can export the current object as text. If this is not allowed, the menu for saving the object is grayed out.
In case you don’t have access to the database for automatic export and import of objects, you can always save the text object to a file. If your report was opened from a text file, you can save it to a text object file. On the other hand, if your report was opened from an RDLC layout, you can only save the RDLC to a file. This is what happens if you opens the designer from C/SIDE with view->layout.