Instead of --user, pass --chuid in init script. baselayout-1 is still default and stable, I think it should be support prior to openrc. (no idea if detection openrc is possible atm)
Should be fixed in transmission-2.10. Actually I have no setup to test it as all my systems migrated to openrc more then year ago, so please, test it and tell me if it works for you or not. Note, 2.10 has quite mangled init script but it should be much easier to understand then previous one. It has only three configuration options in conf.d file: TRANSMISSION_OPTIONS - options for transmission-daemon, logfile and runas_user (which is now required and default to transmission but you may change defaults, of course). Enjoy.
Thanks, will test on my HTCP at home. Cheers.