Yuppp
What if, B1's run ends at the B-10, instead of the B-40?
OK, then the penalty will be enforced to the B-5, there still is no real choice. The foul doesn't go away just because it happened in front of the basic spot.
Or the original play occurs during a down in which time expired in a half? Are you going to deny Team A the choice in those situations?
Now you have added another element. Am I ever going to deny A a true choice if one exists? Of course not. But in the original post, no "choice" existed.
But even in this end of the half scenario, if B has any sense at all, then A still isn't going to have a choice. If B declines A's foul, then A will decline B's foul and the half will end. And if B is stupid enough to decline A's foul, then A still doesn't have a practical "choice".
Imagine that conversation with A's coach: "Coach, you can accept B's foul, where they will have the ball at their own 20 with an untimed down. Or you can end the half." Is there a choice?
4th and 1. A is at the line in a long count. B gets anxious and jumps offside. Are you going to stop and ask A if they want to accept the foul?
A throws a long pass downfield, where B inteferes with the receiver. The receiver makes the catch and runs into the end zone for a TD. Do you want to ask A if they want to accept the foul?
Some times if best to be RIGHT over PRACTICAL.
Often, they are the same thing!
None of which gets back to the question James asked in the original post: there in no "tack on" for A's foul. Either B accepts and they offset, or they decline and keep the ball after the enforcement of their foul.