Nice to see this thread still alive.
A random idea just popped into my head (looking at a post that someone commented on that @hugo wrote a few years ago mind you!) would be around the idea that categories are really only useful to people who are actively using them to achieve something.
As per the last two responses above. Is one step towards custom categories to simple leave the NUMBER of categories as it is, but let us rename/icon them?
I don’t use ‘Travel’ as my bus pass is a fixed monthly price, so let me use that for ‘Lunch’…
Then you don’t really have to change too much in the current implementation, as the number isn’t changing, and the reporting still works, so even the budgetting would work (presuming the label change is passed through to there as well)?
Just a thought.