[Question] Knox and custom rom topic

Hello,

A friend of mine have a Galaxy note II N7100 with android 4.3 N7100XXUEMK8 so with knox crap
How could I install a custom recovery on his device (e.g. TWRP) so I can install custom roms such as SlimKat please ?
He don't have warranty so nevermind if it's voided

Thanks