C# web add table to linq to sql file problem

Question

For a C# 2010 web form application, I dragged a new table onto the *.dbml surface. When this occurred, the .net framework changed the exisiting connection string to a default one that it came up with

instead of using the existing connection string.

Thus to resolve this question, I have the follwoing questions:

1. When I drag a  new table onto the .dbml designer surface, how can I keep the .net framework from changing the existinng connection string and use the existing connection string?

2. For an existing .dbml file that I already dragged the table onto the .dbml designer surface, can can I fix the exisiting code so I do not need to recreate the code from scratch again?