The moost stressful string changing I had to do was 2 weeks ago while accompanying a bunch of primary school kids exams.
Everything was running smooothly & well on time for the 1st 9 entrants. I then realised as I went from exam room to practice room & back again that the last 3 violin entries hadn't turned up (despite letters to parents saying they had to be there at least 20 minutes before their exam time. Asked other waiting parents to try & contact missing ones by mobile - eventually they arrived and I hurried the 1st in to the practice room to tuneup & warm up.
Now this particular child had told me at the school gate on the Monday (the day previously) that the E string on her violin had snapped on the Saturday & that Mum was going to get one that day. (What about the letter sent out 6 weeks previously reminding them that they each needed a full set of spare strings?).
Not good, I thought, as this child wasn't able enough to spend 3 days immediately prior to the exam without practising. Child said that mum would put on the string (she plays the violin too) & I'd said any problems just phone & I'll do it for you.
So child fishes out violin & proudly says that dad put the E string on the violin........
indeed he had.....

he'd taken out the fine tuner, jammed the screw through the loop of the E string & screwed the fine tuner tightly back into the tail piece

. I couldn't believe what I was seeing; this child is supposed to be doing an exam
now andher violin is unplayable as it it. (Foolishly) I have omitted to bring along my own violin. She can't play 1 of the other children's because hers is fullsize & theirs are 3/4 size.
You can only imagine what I was thinking as I frantically tried to unscrew the fine tuner to get the E string out and put it in its correct place. And how I was thinking it will never stay in tune even if it's restrung correctly. I couldn't even have put 1 of the other children before her because I had to have a runthrough with them & accompany & there was no-one else to fix the string in that time.
I did actually manage it & she played as well in tune as she was likely to do so she was fine about it. Not surprisingly my nerves were in tatters after that....