If we would like to offer players/modding community option to extend the mutable parameters values in customizable object, how should we approach it correctly?
Is the Mutable tech ready for modding? Does it already support modding through data registry for example? We would like to combine mutable modding with GameFeature plugins.
Mutable is not mod-ready. The primary issue is that you would need to recompile the graph once you registered new assets and that is something that you do at cook time.
The closest we have to modding right now is the new dataless assets feature in 5.7. With these, you pass in the assets you want to use as data, and the output is the model. The feature is highly experimental right now, so we recommend trying it out, but not using it at the moment. That said, it removes the need to recompile the graph, which could serve your needs, but depending on the extent of the modding you want to do, there is most likely still more to do.