Succeeding Spot Enforcement
 

a) 1st and 10 from the A20. The clock has 0:02 remaining in the 2nd quarter and the clock starts on the snap. A5 breaks free and runs 80 yards for the TD. During the run, A5 taunts B10. Time expires on the play.

Can B accept the penalty and enforce it on the kickoff in the 3rd quarter?

b) A trails 14-7. 1st and 10 from the A20. The clock has 0:02 remaining in the 4th quarter and the clock starts on the snap. A5 breaks free and runs 80 yards for the TD. During the run, A5 taunts B10. Time expires on the play.

Can B choose to have the penalty enforced on the succeeding spot in overtime (assuming the try is good)?

Both A&B are fouls by the scoring team. They are also live ball USC fouls that are treated as dead ball fouls. In both cases if they are excepted they must be enforced on the PAT. Only fouls by the opponent of the team scoring a touchdown may be enforced on the ensuing kickoff.

Canadian Ruling
 

CANADIAN RULING:

1. Taunting is always applied on the succeeding spot, including spanning quarters. TD counts. The foul could be enforced on the try, or the KO to start the 3Q, at B's option.
2. Taunting is always applied on the succeeding spot, including spanning quarters. TD counts. The foul could be enforced on the try, or the KO to start the OT, at B's option.

I remember discussing this before that this is the case. I just couldn't find it in the rule book. Only live ball fouls carry over, right?

So, instead we have:

) 1st and 10 from the A20. The clock has 0:02 remaining in the 2nd quarter and the clock starts on the snap. A5 breaks free and runs 80 yards for the TD. During the run, B10 punches A25. Time expires on the play.

Obviously B10 is ejected. Can A accept the penalty and enforce it on the kickoff in the 3rd quarter?

b) A trails 14-7. 1st and 10 from the A20. The clock has 0:02 remaining in the 4th quarter and the clock starts on the snap. A5 breaks free and runs 80 yards for the TD. During the run, B10 punches A25. Time expires on the play.

Obviously B10 is ejected. Can A choose to have the penalty enforced on the succeeding spot in overtime (assuming the try is good)?

Unsportsmanlike penalties and dead ball penalties can be carried over from the 2nd quarter to the 3rd quarter and from the 4th to overtime. However both of your situations would not carry over as overtime does not start with a kickoff and the 3rd quarter kickoff is not the ensuing kickoff after a score at the end of the second half. A kickoff may be the next play to start the 3rd quarter but it would have happened no matter what happened at the end of the second half and is not a result of the last play of the half.

Both of these must be enforced on the try. Unless you want to be the first out there to have an untimed kickoff.