Making custom category in AddressBook

Is there a way to do this via AppleScript?

Try this:

tell application "Address Book"
	set thePerson to item 1 of (selection as list)
	make new address at end of addresses of thePerson with properties {label:"Palindrome", street:"123 Anystreet", city:"Anytown", state:"PA", zip:"99999"}
end tell

Introduction to Scripting Address Book

Or maybe something like this:

tell application "Address Book" to set allContacts to name of every person
set chosenContacts to choose from list allContacts with prompt "Use ⌘+Click for multiple selections" with multiple selections allowed
set newName to text returned of (display dialog "Enter a name for the new group" default answer "")

tell application "Address Book"
	set newGroup to (make new group with properties {name:newName})
	repeat with i in chosenContacts
		add person i to newGroup
	end repeat
	-- relaunch is necessary to update 
	-- (at least on my computer)
	delay 1
end tell

Hope it helps,