I’ve read 2 interpretations of the new rules:
1) you’re only locked in if A) you’ve played 4 senior international games , or if B) you’ve played a senior game at or over the age of 21, or if C) you’ve played in a major tournament.
2) a) same c) same b) if you’ve played a senior game or competitive underage game over the age of 21
There’s hasn’t been any examples to test the rule so far but the likes of Gallagher and Coventry would be people who are eligible to switch under criteria a but not criteria b.
I guess time will tell which interpretation is correct