Some proper discipline is needed here, it has been long proved that "soft hand" treatment to yukkuris without them earning it will just ruin them, you Hard Love is always needed to avoid them being ruined for good and fall on the shithead side of the easy.
Well depending of the author's yu fanon, the owner could force feed the yu with non sweet food until the taste spoil is neutralized. Some authors don't make taste bud spoiling a definitive ailment that dooms the yu (let's face it, it's doom them, not even pet yu's eat sweets 24/7 and if they refuse to eat anthing else they'll starve)