I'm not an TD, but I "think":
1) Yes, south can bid again. After 4
♠ he can easily know that he misbided. Also his partner can find out what happened. Especially if it is not an expert level bridge (they don't make mistakes
) These things sometimes happens to me also. And I always select the less favourable of sensible bids for us. But to stay in 4
♠ is clear non-sence. I think that the information was of low use here. (I don't think that 4
♠ should be taken as shortage, but if yes imho in this case 5
♥ is also right bid)
2) Nothing to rule. If they play 5
♥, everyone should know what happened. I don't even think that the declarer should warn you before lead (but it would be kind). I make an exception to this: I would adjust score if the opponents were really begginers and there is suspicion that they could not find out what happened.