Ewesful, I'm 20+ years with a colostomy (yes, left side) and my GP agrees that there is a distinct risk of serious damage to the stoma in a crash where a seat belt is in use (I have a note from him which I carry with me in both cars). I have also noticed issues related to chaffing and irritation at the site. I found that after about an hour of driving, the seatbelt would cause a blockage (as the waste simply could not exit my stoma with the seatbelt in place). During longer trips, the discomfort from the blockages would be moderate to severe!
As for adjusting the seatbelt, this simply doesn't work: the seatbelt is designed to cross the hip/lap and thus the region of the stoma, so, to place it higher or lower would certainly cause damage (see owners' manuals on proper seatbelt use)!
I live in Ontario, Canada and get all of my supplies from Shoppers Home Health (who speacialize in ostomy care). I have asked the staff and queried a supervisor on this topic but they could NOT locate any workarounds for my issue. I will ping Convatec to see about Stomaplex.
This is a very personal decision which I've researched and made with my family understanding the potential risks. The ultimate decision rested on the likelihood of damage to the stoma at relatively low speeds (where the edge of the seatbelt might be under the stoma), given the absence of nerves in the stoma it's likely that you wouldn't know you'd been seriously injured. This sort of stop/start driving happens frequently while driving around so the concern, in my mind, isn't about during crashes.
The only time I wear a seatbelt is when I'm flying as I don't want to become a "missile" whenever there's turbulence ...
Do your own research and ask a million questions as there are no experts on the topic!