First and foremost try to follow PEP8 standards for naming variables
From my understanding what you are trying to do is, while seeing in admin / user defined page this field must display APP_SERVER\(Prod\)
in this format.
For that better to keep you variable name as app_server
and while creating ModelForms
in forms.py
change the label
of the app_server
field to APP_SERVER(Prod)