Rewiring Power Distributor -- Will Silver Plated Copper Help or Hinder?

you can try this, with as many woven strands as it takes to get to 12awg in equivalence. Each end must be soldered so as to avoid intermittent or lesser contact with each strand as a potential problem area.
https://www.awcwire.com/part.aspx?partname=e18-7
it's 7 strand, for  less bass, more highs. go to 19 strand for more less highs, more mid and bass. or mix the stranding types. but not the overall awg of each strand.

https://en.wikipedia.org/wiki/American_wire_gauge

The awg chart says that 4 woven strands of the 18g will get you to approx 12-11 awg overall strand sizing area. Put a skin on it to keep it clean and safe, and remember to solder the ends.... and then form into a hook to go around the screw terminal of the AC power socket termination points.

It's a fairly inexpensive way to experiment.

Silver plating is used to deal with long term copper oxidation issues in some applications. That’s part of why it tends to be the spec part in aerospace applications. Aircraft, military, etc. This does not mean it is perfect for home audio. Some like it, some don’t. 7 strand configurations sound different than the 19 strand configurations.

The last time I played with this, which is back in 1990-92 or so, I was making woven multi strand and multi-awg power cords and speaker cable from belden’s best silver plated copper, with 600VAC rated Teflon skins. I’ve still got some of it kicking around... I was using 4 different gauges, woven, IIRC.

At the same time, I was making interconnects from silver plated copper RG-62 cable cores, and with 4 core strands, woven. A rg-62 core, in some RG-62 cable designs...is a silver plated copper wire, with a Teflon or poly strand woven around it, to keep it away from the outer poly semi-hard skin, so the wire is supported by a good dielectric -- and then surrounded by air. Sound familiar?

I sold them through Glen Sinclair, of Audio Two, down in Windsor, Ontario. He sold them into the US. I sold about +50 pair like that. They went all over the upper eastern seaboard of the US. I guess people liked them. Audiophiles are talkative about things that work and sound great. Anyway...some years later.....this particular interconnect configuration arrives as a new thing, via some company....

Copper oxide sounds worse than silver oxide, as well.

Pure silver would be prohibitively expensive. But probably an excellent choice.

High final AWG (eg, 10/12awg) complex multi-strand sized and type speaker wiring would be most beneficial, but is not AC power rated. Nice idea, but don’t do it.

I'm aware that silver plated copper isn't always liked when used with interconnects and speaker cables, however, I don't know the effect when you are speaking of power distribution. I'm sure you realize your long break-in of the Porter Ports was due to the cryogenic treatment which always takes a long break-in time.
You might want to contact @Ozzy and @Grannyring here on Audiogon because I know they have experience when it comes to rewiring power distribution units.

How is pure silver v pure copper in this application?

I've never had good luck with silver plating. After a few weeks it finally settles down to sound as good as copper. IMHO, not worth it. 

Use pure silver or pure copper.