Is it legal? – 3

You open 1N and partner bids 2D. This requires you to bid 2H and over this partner bids 3D. You have agreed that now this shows only diamonds and is to play, so you pass.

Surprisingly, this is permitted, even at OB level 2.   BUT BE WARNED … Pretty much the whole of the bridge playing world, including the Director and his pet poodle, play this sequence as a one round force promising at least five hearts and four diamonds.   If you insist on playing this way, therefore, you will have to make this abundantly clear on your convention card (and in answer to any opposition questions) to the satisfaction of a disbelieving director and possibly disgruntled opponents. You must not describe 2D as a "transfer" - since it does not guarantee hearts. You should say that it either shows hearts or a desire to play in 3D.   Furthermore, you must alert the 3D bid, otherwise your opponents will be entitled to expect it to be forcing.

If, despite the problems, you get your kicks out of quoting - Orange Book 12.5.3 “all continuations (after a 1NT opening) are allowed ” – to the director and have him scuttle off to check this out before reluctantly agreeing with you, then this agreement may be for you!