Adjusting Scanning Rules for Different Domains Hosted?

[Forrest Aldrich]

I host multiple domains on my server; I was asked recently if I could 
adjust the scanning rules on a per-virtual-domain basis.   To me, this 
doesn't make sense, but it's not something I'm able to answer.  Anyone 
out there have this type of issue with their setup and SpamAssassin?     
My MTA, currently, is Sendmail 8.12, though I'll be upping that to Qmail 
at some point.

Thanks....