Power Cord CDP Termination

But by running current through some of the old power cord, wouldn't that defeat the purpose using of a better one?

it will still work fine even with the pigtail. If you like the results (and you may wish to experiment with different upgrade cords to determine your preferred sonic signature) then later you can add the IEC, or have a local shop do that for you. Greenlee makes a special chassis punch for just such a purpose. Or you may be able to use a nibbling tool. The Dremel grinding option; I would not advise doing that due to the particles & metal dust which gets into everything & can cause serious damage. The ferrite may or may not be desirable; try it both ways if you try it at all; it will affect your sound. Some cords are already filtered anyway.

My advice here is not to bother, the difference sonically would be minimal, the cost could be better spent on a different cdp.

Best,
Ps

I replaced the cord on my Njoe Tjoeb 4000 (Marantz 4000) by wrapping the power cord with foil and shrink tubing and connecting directly to the block inside the unit. I don't know if it made a difference but it is more elegant.