Can you change skins with the same character?
Absolutely. See the Minecraft internet site, log in, and also you can select your skin as high as you such as. You can visit to a web server with a various skin every 10 mins if you such as. The skin is brought on log - in ; transforming it on the website will certainly not transform it on your video game personality till you log out and also back in to the web server.
It is not feasible to set a skin per web server or map if that is what you are asking. It is per Minecraft account, so as Myrddin states you can transform it as usually as you like, yet it will certainly not automagically be this skin on that particular web server and also an additional skin on the web server there.