Is there anything in mercurial to 'parameterise' values in a file?

[Chris Green]

I suspect this may be outside mercurial but I'm sure that others here
may know of solutions.

I have a file that is common to many systems but has one line that is
configured with system related information (in my particular case it's
the system's domain name, but there must  be other similar cases).

Is there any way of managing this type of thing?

-- 
Chris Green