Title Company on Purchase and Agreement Question

My purchase and sale agreement asks for the title company that will be closing the deal. I was planning on assigning the contract to an end buyer and use the title company of their choice. When I send the purchase and sale agreement to the seller does the title company have to be on there or can I wait until after it gets back and then put the title company of the end buyers choice on the contract?

And under buyer on the purchase and sale agreement it says " and/or assigns" do i need to put my name after that to make it clear im assigning control to the end buyer or can i leave it at that?