Consider letting the operator change the "to" address of rails

This might be helpful in a few situations:

1. Repair: need to start paying some other party.
2. Async deal flows: the operator may want to lock funds ahead of time, but doesn't yet know to whom those funds are to be paid.

I want to mull over this a bit, but I'm filing it as an issue so we don't forget it.

The issue names no files, tests, or entry points. Start by reviewing how rails record and use their “to” address, then clarify the repair and async-flow requirements with the maintainers. Done requires an agreed design for operator-controlled address changes and corresponding test coverage.

Written by the indexing model from the issue text.