Playing only first movement of Bruch violin concerto
In the LRSM syllabus, only the first movement is needed for Bruch violin concerto. However, the first and second movements of the concerto is continuous and without rest. So we just play the first movement and stop in the middle during the exam? That seems to be strange ...
The first movement can be ended with relatively little modification. You just change the A-flat at the end of the run to a G, and then the pianist can stop right there too by playing a G minor chord. It's a little abrupt but the judges will understand.
IMHO, I don't think you should change the last note of the run into a G. It would sound a little odd since at that point you are in the key of e flat meaning you'd be ending on the mediant of the key. I would just have the pianist stop on the next authentic cadence which in this case would be the third measure which the I6 (Eb in 1st inverson) chord.
At least in my experience, it's very common to change the last note of the run into a G, and have the pianist play a G minor choir to end the movement, especially if you don't want to end on the written Ab, and have the collaborative pianist play until the end of the movement.
Depends a bit which key you're going to with your next piece (and, indeed, the character of the next piece).