Has anyone successfully rounded the holes of a Generation whistle without enlarging them. If so, how?
Hmmmm? I don’t know. All the holes on my Gens are already round…except the window. 
Or are you wanting to remove a sharp edge on a hole? That’s fairly strightforward. I’ve never thought a Gen needed that. Some options:
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You can wrap a piece of sandpaper around a dowel or a round pencil so that the diameter of the rolled sandpaper is similar to the diameter (or a little larger) of the hole you are working on. Then just work across to hole and then spin the dowel until you have eased the edge.
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Use a fine abrasive stone made for a Dremel (but don’t use the Dremel). Do it by hand or with the Stone mounted in a pin vise. Take it easy.
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Use an Abrasive pad on the end of a rounded off dowel with a slightly larger diameter than your hole. Twist, twist, you’re done.
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Deburring tool or similar device.
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Mount the whistle on the table of a CNC milling machine and write a routine to ease the edges of each hole. Might be overkill unless you have a few whistle to do this on.
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Buy a nickel plated Gen. They seem to have softer edges, IME
Hope that helps.
Feadoggie
Cross post with Feadoggie, but I believe we are in agreement:
More importantly, why would you want to round the holes any further than they already are? All of the tone holes on the the half dozen or so Gen whistles I’ve owned over the last 30 years have been pretty convincingly round. You would almost think they had a factory somewhere drilling out that thin wall brass tubing with industrial jigs… 
On the other hand, if you are looking to bevel the edges of the outside and inside of the toneholes (as is sometimes done on thicker wall polymer or wood whistle bodies), I suppose you could do this with a carefully applied needle or jewelers file. I still doubt that there would be any significant improvement possible with such a thin wall tube, and you certainly run the risk of slipping and enlarging the tone holes in ways that could affect the tuning.
Not something I would recommend, but at <$10 for a whistle, I guess you could experiment.
Jerry used to keep a spare supply of holes in his workshop. The mouse may have disappeared with them though.
It’s not a mouse, it’s a whale…
It’s a duck head.
I thought he was using them in that test to see how many holes it takes to fill The Albert Hall…
Best wishes.
Steve
I’m afraid the question as it stands doesn’t really make sense.
Let’s start with: What exactly is the problem you think exists, and why do you think it needs to be corrected? Then we can proceed from there.
I thought those were doughnut holes…
Generation whistle holes appear round viewing them from the top looking down in to the hole.
If the bottom of the tone tube were cut and then flatten the tone tube they would be oval.
The holes were made in the non flat surface of a round tube.
To make the holes round would require adding brass or removing brass.
Both ways would change the pitch of the whistle and then the holes would need to be moved.
The round holes in a Meg whistle were made in the flat metal before it was rolled into the conical shape.
Thanks for all the input, guys.
Sure, of course.
But you still didn’t answer my questions:
What exactly is the problem you think exists, and why do you think it needs to be corrected?
Okay, my gripe is that I don’t like the feel of the holes; they feel sharp to the touch and don’t make for smooth bending of notes but I guess I’m maybe going to have that problem with any whistles made from thin metal tubing,
Ah OK, got it.
The relatively sharp edges are a feature, not a bug! But you could use a bit of sandpaper to lightly chamfer the holes (round the edges) without taking off enough metal to affect the intonation.
Maybe I’d be better off with a PVC whistle of some kind.
The material won’t matter. It’s all in how the holes are finished by the maker.
Some people like to feel the holes and they might want an edge. Others, like yourself perhaps, do not want to feel an edge at all. All about personal preferences in the end. The interesting thing to me is that some individuals will play a particular whistle and really notice the edge of the holes and others will say they don’t get enough tactile feedback from that whistle. We all have different hands and fingers, some more sensitive than others I suppose. Anyway, you’ve been given the list of possible solutions. No need for another whistle.
Feadoggie
I am shocked and surprised at you… such heresy… I imagine the thought police are on they way as I write.
I think the sharpness goes after a while. Maybe just a gentle polish of the metal around the holes might help, or just using the butler’s thumb.
… or the callouses develop.
You have a butler to play your whistle? 
Feadoggie
Whistle makers around here use a polishing wheel mounted on a bench grinder and an appropriate polishing compound. That works for brass as well as aluminium and is quicker and smoother than using sandpaper. It will also remove any protective coatings that the tube may have on it.