Both my male bunnys acted as usual after castration. So I didn't do anything special after.
The one I have now (Kenzie) got castrated on my kitchen table and he was so relaxed from the beginning so he didn't have to get the whole dose of the sleeping medication but he also had some trouble waking up when I had him in my lap because he felt to comfortable so had to put him in his transport to wake up, no problem with his appetite thou. https://youtu.be/lHVEFxRNzRc
Turns out Charlie is not a he but a she! Obviously, the surgery was a lot more complicated as a female and although the procedure went well I was very worried the night after. She was refusing to eat and I had to try and syringe feed her but that didn't go down well. Today shes happier to eat a few veggies and hay from my hand but I was very worried at one point.