We know from the torah that eating or drinking on Yom Kippur is forbidden. Yoma (in chapter 8) lists some exceptions that all have to do with extreme need (health). But, aside from pikuach nefesh, we don't eat or drink on Yom Kippur.
I was therefore surprised to learn, in Yoma 6:5, that when the one leading the goat for Azazel stopped at each of the booths along the way, they offered him food and drink. (The g'mara explains that this is if he needs it.) Earlier in the chapter (6:3) we learn that all are fit for this duty; it's not a super-restricted job where there are only a few people who could do it and thus we're worried about one of them weakening and being able to continue.
If the person leading the goat is to tired, hungry, or thirsty to continue, why not have someone else take over? Even though the kohanim made a rule that it has to be a Levi and not a Yisrael, there are lots of Levi'im. Were they all at the temple except the one leading the goat, and that's why they couldn't make a substitution? But, if that's the reason, wouldn't substituting a Yisrael be a lesser transgression (it only violates a human rule) than having somebody eat and drink (which violates a torah law)? Does it say somewhere that one person needs to complete the full journey and substitution isn't possible?