Inconvenient?  Maybe.... but a vaginal infection from a guy doing this is WAY more inconvenient... it'll cost said lady a weeks worth(minimum) of work. So maybe start with the vajaja, and then move to the booty after you're done... otherwise, go wash your hands BEFORE switching back.

Real life isn't pornography.

Anal to vaginal play (A2P) exposes the vagina to bacteria from the anus which can severely disrupt the environment and cause infections which cause vaginal odor among other things.  Its great to masturbate to A2M and A2P play in videos but in the professional life of a provider its not so smart.

You could carry finger cots or cover your fingers with condoms (which I do sometimes during prostate play)...but if you're with an experienced provider cleaning up doesn't have to interrupt the flow of the session.

Personally, I try not to let safety inhibit or disrupt sessions so I plan and set up in advance.

I allow anal and vaginal play but after a client touches my anal area I reach under the pillow to find the sanitizer I've hidden among other "Easter Eggs" to clean his fingers in a thorough but sexy and convenient way. If that isn't possible situationally I just take mental note of which hand has touched where  and re-direct if he'd like to continue finger play.

Good luck - but considerate play makes for a happy, healthy provider.