How to substitute a portion of the text value of an e

I've got an element like this:

<box:base-file-name>C:/test10/user/server/logs/server.log</box:base-file-name>

I'd like it to look like this:

<box:base-file-name>C:/other103/user/server/logs/server.log</box:base-file-name>

I'm passing in an OLD parameter that contains "c:/test10" and a NEW
parameter that contains "c:/other103" but I'm not sure how to
substitute just the OLD portion for the NEW parameter in the value of
box:base-file-name without nuking the rest of the value which I want
to preserve.

Is it possible to just change a portion of the value?

Thanks