using sed to replace two patterns within a larger pattern

Using sed how could I replace two patterns within a larger pattern on a single line?

Given a single line of text I want to find a pattern (Let's call this the outer pattern) and then within that outer pattern replace two inner patterns.

Here's a one line example of the input text:

Z:\source\private\main\developer\foo\setenv.sh(25):     export 'FONTCONFIG_PATH'="$WINE_SHARED_SUPPORT/X11/etc/fonts"

In the example above the outer pattern is /^.*\([[:digit:]]+\):/ which should equal Z:\source\private\main\developer\foo\setenv.sh(25): The two inner patterns are /^[A-Za-z]:/ and /\\/.

Another way to phrase my question is:

Using sed I know how to perform replacements of a pattern using the s command, but how do I limit the range of s command so it only works on the portion of the input string up to the (25):?

The ultimate result I am trying to get is the line of text is transformed into this:

/enlistments/source/private/main/developer/foo/setenv.sh(25):     export 'FONTCONFIG_PATH'="$WINE_SHARED_SUPPORT/X11/etc/fonts"