Not tested, but here's yer fish. Same as it ever was, just drag to your AutoCad, or appload it. All credit goes to ronjonp for his conditional statements.
(defun c:Luke_Dim ()
(cond ((wcmatch (strcase (getvar 'dimstyle)) "*STD*")
(setvar 'dimscale 16)(setvar 'textsize 2)
)
((wcmatch (strcase (getvar 'dimstyle)) "*MM*")
(setvar 'dimscale 406.4)(setvar 'textsize 50.5)
)
)
)