Hey tedb,
I always start with a screwdriver at the junction between the extrusion and tip. Go real easy with the screwdriver against the comptip itself, it will chip. Once you get it started, just grab it and peel it to the head.
Use a fine toothed hacksaw to trim it to length. Yeah, they're all different. I mark them with masking tape to make sure I get a square cut on the track. A chop saw with an abrasive blade works well if you have one. I use a radial arm saw with a small-toothed blade.
Use a file to bevel the sail track so the sail won't get snagged. The Leatherman file size is perfect. Do it before you install it. After you get it trimmed and beveled snap the new track into place. Pin one edge under the lip on the comptip and work your way down. I always exagerate the track down toward the alu/tip junction and fine tune the height with a soft blow hammer to get it perfect. Also, if it looks too long, don't snap the track all the way down, just bite the bullet and take it off while it's easy.
One more thing. Make sure that the lips that hold the track onto the comptip are clear of any debris that could keep the track from snapping into place. A quick hit with a knife will clean out any left over fiberglass/ fairing putty.
Hope that helps!