Quote:
an attempt was made in three separate places to add ink to the cover to make it appear as though the 3c stamp is tied.
Sorry, I can't see it. Please point them out. I can see stray ink on perfs but nothing that ties either stamp.
Here's my perf comparison using the bottom of the same stamp, brightened for contrast. Some black specks, etc. but it does the job:

If it's reperfed, it's an excellent job atypical of older forgers. If anything, I would say the opposite side is reperfed, with tinier pins used. Or are they just worn? Those are certainly rough. But why not reperf that side, too, if that was done to the left? There's a short perf on the right side that could be eliminated by reperfing and the stamp would look better.
The 24c is/could be original but the forger perhaps "fixed" a straight edge by removing the stamp, reperfing it and replacing it. But again, perf hole spacing and size is typically done wrong by forgers, though there are perforators that match US perf 12.
Forgers don't do blind perfs on purpose because collectors don't like them. This stamp was not well-perfed in the vertical direction in any case.
In addition, scissors did exist in 1863. Since this is a commercial cover, I could see a clerk buying a few 24c stamps, but upon returning back to the office, seeing the unpunched perfs on the left and deciding scissors was the better separation method.
As to whether the stamps belong, I think they do. The target killer strikes and inking, rather weak, match that of the Green Bay CDS from what I can see. Targets are common, but if we can find a Green Bay cover of this period using this size target killer, all the better. The 3c is "tied" by the edge stain and worn perfs; no forger would do something like this.
Further, 27c rate to Belgium: who would know the proper rate for this before the Starnes book came out in 1989? The rate to England, France and Prussian mail would be known by many collectors, not Belgium. Most forgers wouldn't even care. A fair number of mailers back in the 1860s didn't seem to know or care, either, for that matter.