I agree with
@Matua , mostly
Players jumping between nations mid-year is frustrating, especially right before a tournament
But don't want to see a situation where a player declares for NZ, doesnt get selected, then cant play for anyone. We need our best players playing to get the best game possible.
I'd propose
By Jan 31 each year, every player is required to declare 1 and 2 representative preferences.
Eg.
Roger Tuivasa-Sheck
1 New Zealand
2 Samoa
4 weeks before a test or tournament, nations select train-on squad from the list of players that have #1 preferenced them.
3 weeks before, they finalise their squad from the list of players that have #2 preferenced them and have not been selected by their #1 preference.
In the above example, RTS can not play for Samoa this year unless he is not selected by New Zealand.