I was actually able to make a non-owner perform a write successfully to a private register, with both a read-write or a write-only policy:
https://github.com/DerickEddington/explore_safe_network/blob/bda1b1d19a7ea1e216a45ec2d795af7e0d136147/mbus/src/lib.rs#L111-L133
(To support write-only policy, it only required a tiny change to sn_client to add a Client::write_to_register_without_read method:
https://github.com/maidsafe/safe_network/compare/0.2.4-0.1.3-0.62.3-0.58.20-0.60.2-0.53.1...DerickEddington:7a980654904ff96c84eb2ec811675cd528b6fbe8)
If this is a bug (that a non-owner can access a private register), should I open an issue in your tracker?
Or is this something that could remain? I think I’d like to experiment with it.