I know what you mean, I used to distribute patches on XRay Engine all the time by just packing only patch files that I wanted to override older files. The difference there was that my patches were all common source formats (models, Lua, configs, audio etc.) there was no Blueprints or UAsset in the middle of it all. UAsset itself might just be one more reason for trouble, they need to be processed to create the final data. What exactly the result is of that I don’t know.
UAssets don’t just act like importers, it’s awkwardly in the middle of not source and not final. I’m not even sure if you can create one externally as a “mod” be it a simple texture replacer, and just drag it into the project to act like a patch. Normally when you manage UAssets in a project there is an entire tracking system in place keeping track of what package an asset belongs to, what data formats it depends on, redirects etc. If it is a mod tool you wish for then I expect trouble.