Guidance needed on B1/ B2 Visa ...port changing options

Hello

I feel this is a great place to find the answer as hundreds of experienced Indians are already on the forum.

My question is: I have a valid 10 years Business Visa to USA ( upto 2022). I plan to be there for long time and I see they allow 3 to 6 months stay on each trip. Is there an option I can change the port ( but not return to India as its very costly to and fro )? Also, for how many days ( at least ) the USA immigration check wants me to be out of the USA ports once the 3 month period is over so they let me enter again for next 3 months?

Please guide...thanks in advance !

Sarita