This question would have be more appropriate if you asked whether spammers could change and become valuable contributors and not necessarily tagged spammers.

The mindset of an untagged spammer is different from a tagged spammer. While an untagged spammer might change, a tagged spammer could decide to continue spamming because he has already been tagged.

Just like the case LoyceV mentioned above. I am not sure the user would have changed and become a reputable member today if he was tagged by LoyceV.