It’s not super simple to save attribute sets, granted. What i ended up doing was iterating all the fields on the attribute set and storing them to a JSON file in a special format which can be read back into the AttributeSet upon load.
This is not super hard to do but requires some code.
Take a look at UAttributeSet::InitFromMetaDataTable you can do the same thing for loading from a JSON file. Storing to a json file is just using the same iterating of fields, but storing them out, which i store into a special struct similar to FAttributeMetaData.