What are the steps to follow to unmount the hair from a bow and install a new set ?
What kind of tools and products do you need beside a new set of bow hair ?
How do you measure/adjust the length before mounting ?
Essentially, the hair is held in place at both ends of the bow by wooden wedges. To change the hair, you need to gently remove the old wedges and cut new ones, then push the hair back into place under the new wedge. No glue is used at all. The length of the hair doesn't need to be super accurate because the bow is obviously adjusted with the tightening screw. As long as the hair is fairly loose when the bow is untightened.
However, this is quite a skillful piece of work - I really wouldn't attempt it yourself with a bow of any value.
I can recommend Matthew Coltman: http://www.matthewcoltman.com - who is very experienced and does a postal rehair service.
Hope that helps. Steven