Thanks. However, that completely ignores the WHY of my questions. 

And is a pretty lousy approach to the how: adding a journal entry for every single entry. (Side note: not sure why QB helpers like recommending Journal entries, everything I've read says they're poison and best to be avoided.)

The correct answer for HOW to change vehicle expenses out of "Other" is to move the category itself (and that moves all the entries).

Only you CAN'T do this if using QB in 'business' mode — which is the default. You have to switch it to 'Accountant' mode which unlocks all the features I've been frustrated that QB lacks for the last year.

Here's hoping QB hires a UX/UI team that can straighten out the mess some day.