The struggle of collecting a urine sample at a medical facility is very real, you described it well. I don't have a solution, just endorsing your description of the difficulty of the process. There is nowhere to place the container safe from tipping and have both hands free to handle the bag.
As far as bag change: I was changing the bag on the morning of the urine collection, assuming that would cut down on bacteria. However, my urine samples had trace of blood. It turns out that when we clean the stoma at the time of bag change, there will be a minute amount of blood. that blood will be flushed out after a couple of bag emptying but not right away. Now I change the bag a couple of days prior to a urine collection and there is no more trace of blood.