I have a Pr4 site and did a 301 redirect on it. I only changed a couple backlinks, but the majority of my backlinks are not changed. Google is already starting to show the new site(not yet with the same rankings). I was thinking that if I switched all the backlinks it would be a bad sign cause google would see it as a spam domain since the other is a fresh domain with no history. Should I SLOWLY change the old backlinks maybe over the next 6 months?