Yes it is . But you need to download a program called WinRaR. First you open ''run'' on your computer. type in %appdata%... then click on .minecraft. Go into the bin>then right click on the minecraft.jar (an icon with a cup of tea name minecraft) then it will open WinRar. Look for the ''mob'' or ''mobs'' folder. scroll down and look for an image named char.png now if you open that picture it will be the steve default skin. Now to change that skin you get the skin picture you downloaded and rename that ''char''. First delete the char.png image... then the skin you downloaded that you renamed to char.. put that in the mob folder. it should now be called char.png. Make sure that Minecraft the game is closed before deleting the original char.png image. So after you placed your renamed skin into the mob folder. Close everything MAKE SURE YOU SAVE and then start up minecraft! Your done with a new skin! If there are any problems please contact me at
[email protected] I believe this solved your quistion of How to have a skin offline singleplayer? If not tell me