This is a deli stoe that has 2 old Cutler Hammer Panels ( Plug-In breakers not bolt-in Type CH ). Each panel has 200 Amp main breaker . The owner install 10 ton AC & Heat Pump roof unit that needs 150 Amp breaker to feed it . What is the best soluation without changing the panel ? Should I install 150 Amp breaker in a box next to the panel and tab the wire to the to the main breaker or bolt it to the bars or what ? And how?

You most likely cannot put a 150A branch circuit breaker in those panels. I bet the max is 125A.

You also CANNOT tap off the main lugs with another wire. This is a BIG no-no.

I'd look for feed-out lugs that snap onto the buss. I am not sure if they are available for CH series. Then you can attach the conductors to that and feed a 150A disconnect near the panel.

What about all the other codes involved with this? Are you up on them?
Are you the electrician doing this job?