need a tip/tutorial

Hello,

i wanted a way to change Cracked Minecraft skin on online MP servers if possible,
and thanks

There is, kinda. If you are using a cracked launcher called mineshafter you can change your skin there and other people using mineshafter can see that change. Other than that, if you only want to change your skin for yourself (not for others to see), then you can change the player skin texture in your resource pack.

You can always buy a immigrated account for like $0.50 off MPGH