Sorry. Must original suggestion was less precise than it should have been. If you are still having a problem, try this for part 1:
On the pole form, add a new field called "Reason" or something similar. In the "help" bubble for this field, explain when it must be filled. In the form, display the field only in edit mode. Also add a form rule like this, which has the effect of making the "Reason" required:
When the record is saved
and all the following conditions are true:
- MR# has been change
- Reason is equal to ____ (i.e., it's blank)
Abort the save ... with the message "Please fill the Reason field to explain why the MR# was changed"
