C'mon Man, Just Leave It Alone

In all likelihood it would just come back without an "original paper" designation. Many early notes, especially large ones, were laundered and pressed for different reasons.

Collectors from earlier times generally did not envisage that improving the appearance of their notes by washing or pressing would someday reduce their value.

Very interesting. I am not sure which I prefer, which just reminds me that I am not a serious note collector.

The biggest difference, to me, is when I compare the boldness of the ink on "The Federal Reserve Bank of Kansas City Missouri" to the left of the portrait on both notes. During the removal of the chopmark, this printed area faded a bit.

Are the paper fibres on the surface of the note disturbed, I wonder, especially in the area where the mark was present?
For $75, your note may well have been resized after being cleaned.

I have always been against cleaning or repair of notes. Apart from anything else, they annoy me by their appearance. It is not a natural thing to happen to a currency note!

I only ever bought a cleaned note twice:
The first time, very early on when I was a novice collector, from a respectable London dealer, who in fairness, hinted at UNC but did not actually grade the note - a pressed EF pretending to be an UNC, which was pointed out by another dealer subsequently.
I learned how to grade after that ;)
The second instance was a very rare note which I was missing and was quite obviously washed, but if you don't have a rarity you buy it! This note doesn't annoy me when I look at it in the album.
I have only seen one other example since then.

Not to my knowledge.
Any instances of spot cleaning will likely either remove the sizing of the note in that area, leaving a portion of the surface of the note which is 'different' (not necessarily lighter) in texture to the rest of the surface, or an abraised area. Damage of this kind would be easily seen if the note is examined at an oblique angle to the light.

This stuff was fashionable in the 1970s. A lot of notes were damaged in those days by cleaning.

Sometimes notes were left with the scent of bleach or some similar substance. Other times the person cleaning the note would use too high a concentration of cleaning agent and the note would disintegrate! I came across one such note on ebay a few years back on ebay, from a batch of quite scarce notes which had mould. Cleaning was attempted and the result was a disintegration of some parts of the note! The note had been up previously prior to cleaning and I had a scan of it saved. It is now a good example of why to not clean notes.

Regarding the $100 in the original post, in my experience a circulated note like that one would have microscopic dirt ingrained on its corners. If the dirt is not present, that would be a good indicator of possible immersion in a liquid.

Curiously, I have come across an instance of a note graded as CU62 (again on ebay), with the following on the reverse of the info slip: "Comments: Rare in UNC! removed ink spot-back".
A cleaned note cannot be UNC imho, AU55 at the very best.

Can I assume by (re)sizing you are referring to the same material process used in fabrics to fill, strengthen, protect, and otherwise alter the feel of the material?