Is this even possible? I guess you could increase the time delay per post, but not sure if you can cut it off after a certain amount for a certain amount of time.
If you see someone spamming, just report the post or user (bottom right of profile) and a mod will delete their posts.
I don't care so much about the rule, so I'm neither for nor against it. Just gets annoying when people keep making threads about users spamming when all they have to do is report the post...