Find and replace m2 and m3 to subscripts

Now I change m2 and m3 to what on the clipboard.  But that doesn't work when I have m2 and m3 in different colors and different fonts tru the lay-outs. 

How can I find and replace m2 and m3 to m subscript 2 and m subscript 3?

Only m2  not 2 alone.

Many thanks