Simple Lisp or Macro to change the units of a Dimension:
(command "_dimoverride" "_dimlunit" "4" "" pause
"") ; Set to Architectural
(command "_dimoverride" "_dimlunit" "5" "" pause
"") ; Set to Fractional
"1" is Scientific, "2" is Decimal, "3" is Engineering, "4" is Architectural, "5" is Fractional, "6" is Follow Windows Format.
If you want to select more than one dimension at a time, you'll have to use (ssget) in place of where the [pause] is in the command.