Yes and no. There is a bit of leeway with the connection string section, but
it is not an external editor and you would have to put the bits in to allow
changing them. On install, however, it is quite easy to ask for the
connection string and even test prior to completing, so there is little need
for the end user to whack the string. You also have the ability to put
config elements in a separate file, which will not be locked down during
runtime, but there is no visual editor, per se.

I am sure there are some instances where end users need to move from one
data store to another, but it is not the most common scenario. I have yet to
have written an application where the common end user flips a connection
string after an application is installed, except for applications where a
user might work with multiple databases and that is usually configured at
runtime (although the strings might be stored at runtime for reuse).

Hope this helps!