If responder has a single-minor slammish hand, the auction starts with Stayman, then the minor ---or (if agreed) the Walsh Relay which begins with 2♦, and then negates the heart transfer before launching into the minor suit slam try.
A) Re: the Walsh Relay, what happens when Opener makes a Super-Accept ?
1NT - 2D!
2H - 2S! [ Walsh Relay , negating the ♥-transfer; thus giving another way to bid 2S ( for the minors ) ]
But if Opener Super-Accepts:
1NT - 2D!
3H - ?? Now what ?
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B) I don't understand bidding Stayman and then 3C/3D to show the long minor, slammish .
Are you saying 3C/3D negates any interest in a Major ?
Normally ( Baze convention ):
1NT - 2C
2H - 3C/3D ( no fit for ♥, have 4oM, ♠ here, and a good 5 or 6+ bid minor, slammish )
?? ( Now if Opener were 4-4 in the Majors, he would bid 3S next )
It looks like your "Stayman treatment" would eliminate finding a Major fit if 3C/3D negates interest in a Major.