I thought it was snc_internal, not snc_external?
Anyhow, I cannot really comment on how you need to implement it, because I do not know your instance.
Normally you could just add the snc_internal role as role in an ACL. I would be more cautious with snc_external, because this would potentially open up your users information to a wider public.
If possible I would add a script in the new ACL, to make sure you are only opening access to users which are used as item owners.
Help others to find a correct solution by marking the appropriate response as accepted solution and helpful.
