relinking P2 media at new resolution

Help! Here is my dilemna that I'm hoping to explain well enough for someone out there to help me with. I am editing a video that was shot on P2 cards in HD (1080I/60) and then transcoded to dv25 for editing. Final mastering is in 16x9 SD. The problem I'm running into is that there is a ton of footage where a host is Chromakeyed over backgrounds and, even using the spectrakey, I am getting dv artifacting which I have been unable to remove. What I would like to do is somehow bring in all of my host footage as either 1-1 or dv50 so that I can pull a better key. How do I best do this? I'm assuming its some combination of unlinking and relinking to the P2 material. Do I have to transcode everything again or can I create some kind of link from my edited sequences to the P2 material which is all stored on an external hard-drive? I'm on an adrenaline using 2.81 software. Any help or advice would be greatly appreciated. DAN