Hello guys I am trying to change nbt of a player who is offline on a server

Are there any way to do this ?

have you done any research at all before, i suggest you look at the forge wiki as there is some valuable information.

Yea I had a look into the wiki...

I do it all the time but there is no information on this on the wiki or I missed

Maybe looking in EntityPlayer class ? 

/* ================================== Forge Start =====================================*/
    /**
     * Returns a NBTTagCompound that can be used to store custom data for this entity.
     * It will be written, and read from disc, so it persists over world saves.
     * @return A NBTTagCompound
     */
    public NBTTagCompound getEntityData()
    {
        if (customEntityData == null)
        {
            customEntityData = new NBTTagCompound();
        }
        return customEntityData;
    }

you missed it

 

http://www.minecraftforge.net/wiki/How_to_use_NBT_Tag_Compound

These are all while player is online...

I want to be able to save into player nbt while player is offline...(NOT LOGGED into the server)

oh... well no one really did this before, but youd have to look at how minecraft handle the .dat fileaand how he converta them in java objects