What do you mean with false positives?
Adding someone elses bitcoin address (as watch only ofc) will create wrong assumptions when someone wants to detect which address are yours and how much bitcoin you have.
Is this a feature of Multibit? I'm not aware that this can be done with Electrum, for example. Or do you speak about posting addresses? Sounds risky, if such address can be connected to other addresses that belong to a spammer then you might get red trust. Of course one could simply use an address from a websites wallet.
You can do this with Electrum, I posted a link above.
I nearly did not find your link about the cold wallets but the link about false positive addresses i can't find at all. Can you give the link again or point me to the thread you posted it in?