The fact that Thorax, as a regular changeling, didn't need to eat anymore, implies heavily that changedling diets did not change. They're all just acting like Thorax did before he transformed. The hunger did not stop because he transformed. He stopped starving when he began making his own love. But he was also being loved by Spike and others, all aimed at him and not someone he was pretending to be. The show leaves it all up to implication, but I imagine that a changeling would starve to death if left in isolation. Lasting longer depending on their self esteem. They're a hove of lovemakers now though, so it would look like they just dont need it anymore, despite their entire species specifically being said to need it. I don't think we should assume they're not feeding anymore. We should assume they are just always full.
I’m pretty sure Changelings don’t feed on love anymore since there hasn’t been anything that suggests they do while at the same time it’s been shown that they eat food like other creatures. Just felt that needed to be said.