You can create a script that appends the existing contents of the field ('Self') to the text "Arr:". Then make that a script trigger OnObjectExit on that field.
Though I think I would check first in the script that the first 4 characters aren't already "Arr:", so that you can edit the field (perhaps to correct the mis-spelling of a name) without adding the prefix twice.
Although that solution is actually modifying the field data, not just 'displaying' it differently. You could create the layout item as a merged field, such as:
Thank you so much! I'm gonna try this one.