Unfortunately once a coin has been altered, it loses much if it's numismatic or collector value, slabbed, and graded or not. Notice it was labeled “Tooled, UNC Details”. with no specific grade mentioned such as MS 60, MS,62, etc. What is not said on the slab is just as important as what it does say on the slab. It is in fact not assigned a grade number because grades cannot be assigned to altered coins, therefore “UNC details” . I suspect your example was once mounted as a piece of Jewelry leaving “tool” marks in places around the perimeter. In the end it is worth what somebody is willing to pay for it. I am afraid you must start at melt value. Some perspective for you : I had a 1916 20 Yen gold coin that was not altered and in about MS 60 and possibly MS62 condition. Stunning coin visually but those that were interested in it were reluctant to offer anything beyond melt. I would rather keep the coin even though I do not collect this type. You can see my example in the photo of the edge in the Numista link to it. Only unaltered coins in the higher grades of MS 62+ do you see buyers offering premiums much higher than melt values. Good luck with your coin.
N#15208
Japan • 20 Yen - Meiji