You may have an agreement with Pershing, and it probably contains provisions for terminating their service. They may require advance notice. First read your agreement. I would discuss with Schwab second, and then when all is ready, contact Pershing.

As to profiling MDP, its best to discuss with Schwab. If it involves restructuring your whole portfolio, some items may be best retained for a while. For example, bonds are better held to maturity. Doing it all at once could incur expenses, that you may want to spread over several years.

I think you will find that doing the individual changes yourself will get the job done at the lowest commissions. Schwab may be willing to take care of it for you, but perhaps for additional fees.