Hi Pissy!
Glad to hear the TKR is coming along and you're getting off the meds.
Hard to get a nicely spec'ed system these days due to the super high price of memory and GPUs, so the DDR4 aspect of your system isn't a surprise. I'm hearing many builders are installing DDR4 as an interim move while awaiting sanity to return to pricing. I think I ran COD5 on a 660 long ago, and it was totally capable of running with max visuals, so even if you wait on the GPU, you'd probably be just fine.
As for the clan tags sticking, I'll make the recommendation I always make - run the game as an Administrator. It may be trying to save the tag information, but Windows is denying the write (save) operation for some reason, and that can be overcome by running the game as Administrator. It means you'll get a UAC prompt confirming you are okay allowing the game to run that way, but it seems to overcome some of the odd behaviors I've seen. All that said, I've also heard from some others saying they do that, but it still loses the clan tag anyway. I'm just really not clear if they really are running the game as an admin or not. I've never had an issue with clan tags and I've always ran the game as an Administrator.
In Windows Explorer... [I'm doing this in Win 11, but this is pretty much the same in all versions of Windows.]
Hope that helps. Kill 'ya later.