If you are just changing a few dimensions with in the drawing you can
individually change that particular dimension settings thru the
properties dialogue box.
Grip the dimension > open the properties dialogue (ctrl 1) > go to sub
paragraph (Lack of better term) called "Primary Units" > Look for
the two Items, >first one called "Dim Units" change from
Architectural to Fractional > than look for "Dim Suffix" and add
double quotes for the inches.
You can create a Lisp routine for this. I have one but it is not
clean. You are welcome to it if you want.