Set class on checksum change

[Adam M. Dunn]

Question:
  I need to be able to define a class when an MD5 checksum changes.  This
is so I can have a class executed only when some files change.  How can I
do this?  The define option of the files action states that classes are
not defined on warnings.  And the MD5 option says changes are only 
reported as warnings.  This tells me this won't work.

Any ideas out there?

thanks,
~Adam