But what if...the feds seize the ballots, say they conducted their own count and announce that the results as given by Fulton County for the 2020 election were "horseshit" (to use the immortal word of wzambon), what then...? Couldn't that create a path by which the feds, either directly or indirectly through the State, could, with the right sycophants in the right places, monkey with the 2026 election results to suit themselves?

What would the path be? There are no competitive races in Georgia this year. At all. Cook Political Report, as an example, has every race as either Solid D or Solid R:

cookpolitical.com - House race ratings

Trump lost most of his election cases in the SCOTUS, and has lost most of the cases he's brought on various matters in the lower federal courts now. Even with judges he appointed. The judiciary may be more favorable to Republicans and conservatives on the whole than it used to be, but there's zero indication that any of these judges have moved into the "anything goes for our guy Trump!" category.

That's why you have an independent judiciary. Not only do none of these judges depend on Trump, or the continued favor of the Presidency in general - they all have their power only as long as we don't lose free elections.