Seems to me rather than mung up the original, just buy a 5 string brass or bronze modern tension hoop and be done with it...

GO-FOR-IT. I have filed several hoops to accommodate me and my playing. banjered

I agree with buying a modern replacement. They are inexpensive and you can likely sell the prewar tenor hoop for several hundred more than a modern one will cost. I think the prewar tenor tension hoops sell for around $600-700 right now…don’t quote me on that. Hopefully someone who deals with prewar parts more frequently than me will chime in on the value.

Is it original ?
Is it brass or pot metal?

If you sell the original tension hoop now, that devalues the banjo if you were to sell the banjo later. 
 

if you never sell the banjo later, might as well file the notch now and enjoy the banjo.  Careful, skillful work, not butchering it. 
 

If the concern is to keep this utilitarian instrument original to satisfy some museum oriented opinions at the final estate sale,  that train has left the station.  

On the topic of original prewar Gibson tension hoops from the late 20's to late 30's / early 40's -
those are absolutely valuable and most would probably agree that changing it in any way will certainly detract from it's value. They are in fact bringing darn good money right now. A typical hoop (Now keep in mind we are talking about a standard, pot metal tenor hoop, with nickel plating) will fetch 500 to 600 dollars. A very good one will fetch closer to 700 dollars. The brass E 2 style hoops, for whatever reason, always will fetch just a bit less. Anyway, there you are. To me, it makes a lot more sense to replace the original hoop with a reproduction or newer 5 string tension hoop, that probably will cost around 100 bucks or less.... and keep the original as it was, and of course keep it with the banjo. IF you decide to sell or trade that banjo down the road, the new owner will want that original hoop included! Part of the reasoning for doing it in this manner is practical, and it keeps the original parts "original." The other reason, is few people set up a banjo to "Bela" specs, and will not have the problems you experience with the wider spaced, taller bridge, that Bela uses in his setup. Another possible fix to your problem is IF there is room, you might check on trying a different head on your banjo. If you could get the head mounting band to sit just a bit lower on the pot and thereby also lower the tension hoop just a hair - you might not have the issue of the strings hitting the "ears" on the hoop.