If you have the patience its better to take it off, then its much easier to do, but it all depends on how handy you are with a tool kit. From there you can use something like a jnr hacksaw or dremel or whatever you can get your hands on and some sand paper (to tidy it up), however i would advise buying a 182 style surround as its never that neat without one. (unless your having a twin pipe fitted in which case you cant)