Welcome Paul - so you think Daniel, having all his faculties, chose to abstain? It seems to me that somewhere in scripture (OT) it says you could not worship/go into the tabernacle if you didn't have all your parts? And does anyone know why they just ate vegetables?
They ate vegetables because it was against the Law. The Law of Moses forbade eating meat that was not butchered and prepared properly.
“If his offering to the Lord is a burnt offering of birds, then he shall bring his offering of turtledoves or pigeons. 15 And the priest shall bring it to the altar and wring off its head and burn it on the altar. Its blood shall be drained out on the side of the altar. 16 He shall remove its crop with its contents[b] and cast it beside the altar on the east side, in the place for ashes. 17 He shall tear it open by its wings, but shall not sever it completely. And the priest shall burn it on the altar, on the wood that is on the fire. It is a burnt offering, a food offering with a pleasing aroma to the Lord."
It was not against the Law to change their names but it was to eat meat not properly prepared.