I am using UPA Java and for ANSI Page payload we could use Msg.encodedDataBody(Buffer encodedDataBody) to encode pre-encoded data, however I am not sure if we can do the same for RWF data (e.g. FieldList)?
Resolver not registered: react.asset.discussionTagsAsset
Yes, a pre-encoded field list can be added to an update message via Msg.encodedDataBody(Buffer encodedDataBody). You must then call Msg.encode(EncodeIterator iter) before writing the message to the wire.
Permission Problem You need the session.valid permission to do that.