"Would Italy be able to convert portions of Ethiopia to Catholicism"
Out of the European colonial empires, only Spain converted most of the natives in their colonies, and the Spanish were both the most fanatical and had the advantage of the conquest itself and following plague destroying the natives' world vies. Everyone else, except the Dutch, did support missionaries and did some conversion but had only partial success at best. And Ethiopia was already Christian anyway.
To answer the question, this is an event that probably would have no effects other than making Italy seem less ridiculous politically. Ethiopia is just not that important. It might well butterfly away the Derg however (
https://en.wikipedia.org/wiki/Derg) and so wind up benefiting the Ethiopians down the road.