As ue4editor help mentioned below, we can use the command "-diff [options] remote local base result" to merge the conflicted file (the 2nd usage)
When I use the command line below (The "D:\fly425\Content\StarterContent\Blueprints\Blueprint_CeilingLight.uasset" is the conflict file, the other two with sha value are remote and base.)
"C:\\Program Files\\Epic Games\\UE_4.25\\Engine\\Binaries\\Win64\\UE4Editor.exe" -diff "D:\\fly425\\Saved\\Diff\\temp-7fe27617ccadc66cf8211441acc099b752087ffe-Blueprint_CeilingLight.uasset" "D:\\fly425\\Content\\StarterContent\\Blueprints\\Blueprint_CeilingLight.uasset" "D:\\fly425\\Saved\\Diff\\temp-1fbe40fd1b8e4ffdc97d624e0fc1ed0d8bfd1d0e-Blueprint_CeilingLight.uasset" "D:\\fly425\\Content\\StarterContent\\Blueprints\\Blueprint_CeilingLight.uasset"
The merge tool window of UE4Editor is show, and I can view the merge view:
But when I click the "Accpet Source" button to resolve the conflict, the window disapeared, but the conflict it still remain. Looks like the merge feature with command line is not available. Does anyone know why?