Don't. It wasn't "ignorant", just overlooked some semantics that "could" give a hint.
It's a real settings-file; now, if only the database-name (or path) is going to differ, it'd might be neat to use a connection-string with a literal set of characters in the place where the databasename should be, and to Replace the literal with the actual path just before using the string.
So, you want the system to do a simple literal replace for you, but you want to roll your own config file implementation? Clever . Are you also going to write all the cool stuff that you get for free with config files such as encryption, versioning, editing through a simple GUI in VS, backwards compatibility, etc?