ditto above

you have two anal sphincters, the outer can be relaxed or contracted at will. the inner sphincter has a mostly involuntary action. pressure coming downwards (ie waste) causes the ring of muscles to relax and let it pass. the inner ring can be "trained" to loosen up, but unless you tear the muscles, usually returns to it's normal elasticity. i don't think there would be any long term fecal incontinence problems, as long as it's kept simple, a lot of lube and a lot of love

keep in mind this is a non-medical opinion.
hope it's of some help