So a bald yukkuri will grow its accessories back in the same amount of time needed for a yukkuri to mature to adulthood, at the cost that it won't grow bigger (or presumably get smarter). Am I close?
No, mister was explaining to Reimu that when she grows bigger, her hair gets longer too, so her hair will grow back in time and not to worry. Anon took off her accessories in an earlier page, and it grows along with the yukkuri.
This is just a different yukkuri setting though. In most settings the hair, accessory and teeth never grow back once removed.
Yeah, that one was done over half a year ago though. Not to mention the whole taking 6 months to grow and its impossible for a yukkuri to live for 6 months in the wild without a hat etc.