In A, the subs can be made anytime -- as said, a sub can enter and take either or both technical free throw, so a substitution needs to be legal there.
In B, check with your local authority. Personally, I hate this practice (one day there will be a brawl that comes from this nonsense), but we have no rule against it here, so I just make sure to be vigilant when the other team returns.
I have more interesting questions, like why the teams always run drills into the one spot on the sideline where I want to stand during warmups?
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