Dimensioning

If you want to preserve the ability to input feet and inches but only dimension in inches:

In the dimension style dialog, set the units to decimal or fractional as required, and set the dimension suffix to the inch mark.

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.