Accepted solution
An alternative option is making all the other tokens write labels on the token that will stay alive after the Join. A somewhat elegant way to do that, is to make the Split activity create the additional tokens as child tokens of the original token and let them write to their parent's labels -- either by checking "Label Access on Parent Only" or by making sure all the labels you want to keep already exist before entering the Split activity and choosing Read / Write Parent Label Access.
Alternatively, you can not allow implicit label access to the parent, but still create the additional tokens as child tokens and then explicitly write labels to token.parent instead of token when you want to keep them after the Join.
