This is a topic that should get more attention than it does. I've been a practicing AB for more than 30 years, so I've encountered my share of messy diaper situations.
Every caregiver will deal with these differently. I've had one caregiver put on a surgical mask because she couldn't handle the smell. Several have (quite properly) worn latex gloves. Only a couple of been very matter-of-fact during a dirty diaper change; both were older than me, had extensive experience dealing with messy kids and tended to see caring for me in the same light.
I think every AB or DL ought to have the 'dirty diaper discussion' with his or her caregiver well in advance of the situation. The plain fact is that a dirty diaper is not always avoidable, but ABs and DLs have (at least, for the most part) the ability to change themselves. As others have posted, I'd avoid 'pushing your luck' - if your caregiver is adamant about not changing you when you're dirty, you should expect to change yourself.
Over the years, I've had several caregivers tell me up front that if my diaper was anything other than wet, I was on my own. However, I only recall one time when a caregiver didn't actually make an attempt to clean and change me. If I've deeply regressed, I'm not always aware that I've gone, and sometimes the amount is negligible. In these situations, even the most reluctant caregiver will just try to clean you up and get you into a clean diaper.
If the caregiver takes changing messy pants in stride, then I enjoy dirty diapers as part of a regressive time. I find that I am still embarrassed as I'm cleaned and changed. If the caregiver is dreading having to deal with a bowel movement, on the other hand, the dread and reluctance tends to show each time they change me. In those situations, I'd rather change myself and allow the caregiver to focus on the more enjoyable aspects of big babysitting.