Unfortunately no, it's not possible to change your channels URL, you can however get a vanity or personalized URL which YouTube will issue you after so long, you do have the option to add a few characters to personalize it a bit more bit even this URL is pretty limited as to what you can do with it.
After that your viewers can either get to your channel via your current address or the one YouTube has offered you.
no that's impossible. except when you changed your youtube channel name then yes. but even then you only can change it into the name you have now. but that's it.