Is that an available endpoint in the dashboard API for SM? I didn't see it, but I miss things...
If it is, then you could:
1. GET list of all organizations you have admin for
2. Filter the result to only the schools you want to touch
3. Find the SM network for each school.
4. Iterate through the SM networks and push the OS update.
For the most part, if you want to manage a bunch of discrete networks all at once, you're going to be using the dashboard API.