If you're going to make a tamer and tame stuff on ice island tame it and then all kill on something or summon a deamon and kill as u tame. Never understood why people tame stuff, rename it and then release it, so much faster to just say all kill & target something and it helps the next tamer.
I don't know if it's the case on this server, but on OSI difficulty went up for subsequent tames. When I played on Napa Valley, there was an unspoken rule, where you renamed the pet a, b, c, or something like that to indicate how many times it's been tamed. To the point, I GM'ed taming off a snow leopard that was either a 3rd or 4th tame (I don't specificially remember). Now, tamers who don't release are just evil.
Difficulty DOES go up after every single time a creature is tamed. That is why they are released, and not killed. They are actually doing a favor, and you should be searching for first, second, and third time tamed creatures. Better chance for a gain.