I’ve opened a similar can to sell individual boxes to collectors and have not yet been struck by lightning or run out of town by a mob, so the moral issues are minimal.
I have fired thousands of rounds of WW2-Korean war vintage .30 carbine ammo and have never had a problem with a single round. ALL U.S. military .30 carbine cartridges were non-corrosive primed so you don’t have to worry about the potential for quick and nasty corrosion in the barrel if you don’t clean right away as you would for most other WW2 ammo which used corrosive primers. If the ammo is all corroded or split of something then I would not use it, but It will probably look like the day it was repacked in 1945 and be fine for use unless it was stuck in someplace getting up to really high temperatures for the last 50+ years.
The Universal carbines have a poor reputation, mainly due to their changing the operating slide design to a dual recoil spring arrangement and making the handle as a stamped part instead of a heavy forged/machined part. The slide handles break quite often and replacement parts are not available (any spares were used up fixing this problem long ago). If the handle fails it should not have catastrophic consequences although the gun will be useless in the future. YOu may want to consider selling it before it breaks and getting a better gun, like a U.S. military example which is collectible (and getting pricey).
Go ahead, open the can- but instead of using the key and strip around the side of the can, use a manual can opener or “P-38” c ration can opener on the BOTTOM of the spam can, so it will display like a full can.