20.- Doublereggers are allowed to play for one regiment, if their other regiment(s) isn't/aren't attending to NWL and the enemy-team accepts the doubleregger for the match
If I'm honest I just think you should remove the bold part of this rule. In the context of NWL, if the player only commits to 1 regiment for the tournament then he is by definition Not a 'double-regger'. It should be no concern of an enemy regiment that one of their opposition wears other tags on other days. So long as the player is not playing for more than 1 team
within the tournament I don't see any logical argument that can be made to claim that it is somehow 'unfair' that this person is allowed to play. The rules should purely be there to make the tournament as 'fair' as possible, not to delve into the complex world of 'double-regging' or the philosophy of what a regiment actually is, these things need to be pre-defined for the tournament by the organisers.