I can't give you any advice on reaming the bowl, other than to be careful. None of my pipes have gotten to that point, and it makes me nervous as the possibility of damage exists.
The most important thing you can do is make sure to put a pipe cleaner or two through after every smoke. Your own spit is the most unsanitary thing about the pipe, and the shank/stem hole getting clogged is your most immediate functional issue. Just get that moisture out and clear the path.
Some rubbing alcohol to clean off and sanitize the stem and pipe bit if you use one.
Bowl cake accumulates at such different rates based on your habit. The moisture of your tobacco and the presence of casings will effect it, as well as dry time between smokes. If a pipe gets used once every two or three days, it should be able to go years without reaming.
I know that doesn't exactly answer your question, but it's all I've got and they're good habits to cut down on how frequently you need to do deeper cleaning