If you have a high output stoma because of what you eat then the answer is simple......only eat stuff that reduces output. But if you have high output because of reduced bowel length then you have to wait until the bowel is empty. What I do is track when my bowels are completely empty and output bile in the morning after I get up, and now know exactly when I have a window to change my bag. I'm extremely short gutted, so my bowels empty fairly quickly and then continue to make bile. Our bowels typically slow down in the wee hours of the morning, and get back to full speed right after you eat your first meal. So you simply have to figure out the latest you can eat the night before and be empty when you get up. For me I have about an hour between bile cycles in the morning, so I typically get up at 7:45am and have a bile output around 8:00am-ish. I then know I have an hour to change my barrier without any output. So it's jump in the shower, dry off, change barrier/bag, and like clockwork I'll see bile output around 9:00am again.
So you simply need to understand your bowel's natural cycle. Taking motility meds is tricky. I've taken them (before I figured out my cycle) before my cycle started and they just extend the time I have bowel output, which really sucks if you're in the middle of a barrier change. Without the motility meds, if I screw up and have bile output in the middle of a barrier change I can just wait it out over the sink and in about 10 minutes it stops. So I always wait until AFTER I see the bile cycle end before taking my motility meds. It takes about 15 minutes for motility meds to kick in, so I can then start eating right after I finish my barrier change.
With my high output the morning (when I first get up and understand my cycle) is the only time of the day I can change my barrier. Now I have changed it in emergencies during the day a few times........but it's not easy or pretty. It basically involves getting on your hands and knees and having a bucket under you to catch the output as you try to keep the area around your stoma clean enough to get your ring and barrier to stick. You end up burning thru a lot of supplies and will want to change it again the next morning just to be safe. So learn your cycle and you won't have any problems changing your barrier on your high output stoma. If you need me to explain any of this better........just shout!!