As OurSacredWar can tell y'all, this happens in my non-fascist Pan-African/Ethiopia wins the Second Italo-Ethiopian War TL. Basically the maximum aid that the Liberian government, African Americans and UNIA factions in British colonies gives amounts to:
Anything more than that might be excessive.
- A Liberian based arms manufacturer under the umbrella of UNIA's Negro Factories Corporation establishing a domestic rifle industry in Ethiopia in 1930 producing slightly-inferior copes of the Krag rifle, the Gehwehr 98 and the Browning Automatic Rifles, all chambered in 7.92x57mm Mauser for logistic reasons and modified slightly for African conditions. This company is established in response to Liberia's mounting campaign against raiding interior tribes.
- UNIA's paramilitary units, the Universal African Legions gain experience fighting the interior tribes in Liberia, and about 4000 of them, supplemented by 15,000 UNIA volunteers from other countries in the African diaspora end up joining the Ethiopians. However, the advantage of these volunteers is a bit overstated, with the exception a handful of former colonial troops & American Buffalo Soldiers none of them except the African Legions has any military experience. And the African Legions in my TL only have practical experience in fighting native peoples with spears, swords and pre-WWI rifles and muskets.
- A railroad company under the Negro Factories corporation expanding Ethiopia's existing ITOL railroad to Jimma by 1934.
- A decent sized (~30,000) group of technically trained "Back to Africa" Caribbean Blacks and African Americans who start up cottage industries and small factories in Ethiopia.
As said by others, there is the question of money, all that cost and Abyssinia was not really rich in any way and the only one that can give loan are the Anglo-French, unfortunely the economic and political dealing of the British, French and Italians with the Abyssinian were regulated by a series of treaty and do this will create a diplomatic fuss.
Plus, well i said, the presence of foreign black people trying to help the local modernize will not really win many fans as they poaching in their economic interest...and i don't even talk about the paramilitary units.
Not considering the social changes that all that will cause...in a nation famous for resolving this with violence, really Abyssinia was more 'A Game of Throne' Land than a modern nation, Selassiè tried very hard to modernize during his time but not only there are limit at one can achieve in a limited period but also what the system can take and a bunch of foreigner (because the UNIA member will be seen as foreigner more or less like an italian or a British) telling them what to do will really not help