The classic meter pan is one and done.
No Poco is going to give you permission to open it up to stuff extra feeders into their meter socket. None.
Most meter pans are so limited in space that one can't even squeeze a Polaris feeder tap inside.
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It's a no brainer to simply set a sub panel using, say, a 100A stab-on breaker -- or to attach pass thru lugs -- again a factory produced stab-on product.
You'll have to dig around for it... C-H has these in 3-phase and 2-pole, 1-phase. They slap on like a C/B... but have no over current protection: just a set of lugs.
Such pass-thru lugs are typically rated up to 200 Amps at 240V.
And with that, your design task is complete.
You simply move at least 2 poles of C/Bs out and push on these pass thru lugs. They should lead to another, daughter panel (sub panel) with enough space to make everyone happy.
The Poco need not be consulted. You still have a 200 Service -- but with enough room for AFCI breakers aplenty.
The pass thru conductors need to stay fully sized for 200A. The daughter panel can have a Main or -- to save bucks -- just MLO.
If the daughter panel uses a back-fed Main push-on breaker -- figure it to be limited to 100A.
The NEMA players are protecting their market by not low balling push-on breakers beyond that size.
