quick challenge question

[BrendanP]

3rd and 10 at A40. A12's pass is complete to A80, and after a measurement, the nose of the football barely makes the line to gain at midfield. B challenges saying runner was short. After review, the ball is respotted at the B49, still a first down. Does B still retain a timeout because they were successful in changing the call on the field, even though it wasn't the change they wanted?

[FLbackjudge]

I can't answer for the NFL, but in NCAA the coach loses his challenge and his timeout.  The challenge is that the awarded first down is incorrect (a spot can't be reviewed by replay except with respect to the line to gain or a score).  The ruling on the field (first down) was not changed, so the coach loses.  I'm guessing it's the same in the NFL, but that's only a guess.

[J12]

3rd and 10 at A40. A12's pass is complete to A80, and after a measurement, the nose of the football barely makes the line to gain at midfield. B challenges saying runner was short. After review, the ball is respotted at the B49, still a first down. Does B still retain a timeout because they were successful in changing the call on the field, even though it wasn't the change they wanted?

I'm reasonably certain that that would be an unsuccessful challenge and the time out lost. The challenge is not the spot of the ball but whether a first down was made or not made.  Of course, you review the spot of the ball to determine if it's a first down or not but if first down / not first down doesn't change, the challenge is unsuccessful.