Detune... if you don't your edges break faster. They catch for the first few days which can cause cracks more.... detuning ships that whole process and is safer. I detune tip to tail... everything.
And I would just go to the hardwear stor... get a file. Then you don't just go at it. You work tip to tail, and from the tip of the file to the portion close to your hand. do about a foot at a time.
Hole the file at about a 45 degree angle and work your way down the ski... hard to explain, but easy to do..