Did the split yesterday and it went fine. The operator could give us a private APN for the old 12, took one call and a form. Allowed networks is now their /24 and nothing else. Rotated the 12 tokens and pushed the new ones through the vendor’s SMS config channel, two cabinets didn’t take it so I’ll have to visit those anyway.
IT accepted the “fenced in until replaced” line, with a replacement date. The tester re-ran his van thing on a TLS unit and got nothing readable.