The bumper cover is really quite simple to remove. I've had one of each generation of OBW LTD's over the years (a 97, an 04, an 07 and now a 2012) and have removed the bumper covers on the first 3, for one reason or another. While each is slightly different, they are all basically the same. I really can't get too specific about the 04, since that was a while ago, and 2 cars since.
At the front wheel arch opening, at the seam between the fender and the cover will be a 10 mm bolt or screw to remove. You may have to peel back the inner fender liner to get at it.
Remove the grill. It basically is held in with clips that need to be pried out, or have prongs that need to be pressured towards each other with a screw driver or needle nosed pliers, while you pull the grill assembly towards the front of the car. You may find a push plug or two.
You'll find push plugs under where the grill was. Pry up the centre portion a quarter inch or so, and then pry the whole plug up and out. Along the headlights there may be one or two 10 mm bolts that need to come out, depending on the year.
From under the car remove the 10 or so push plugs (same as the ones on the top).
Now unclip the fog light wiring connectors from the fog lights, if you have them.
The bumper cover should simply pull straight forward off the car.
When you go to install the cover, tape or zip tie the styrofoam bumper filler to the front bumper bash bar, to keep it in place. It may fall off otherwise, and you'll not get the cover to fit.
Tape the edges of the cover with masking tape where it meets the fender seam, to prevent scratching the paint. Remove the tape only when you are ready to push the cover back into place along the fender seam.
Prep the cover for paint with 600 grit paper. The shine must come off the cover and appear dull. The cover then needs to be wiped down with a degreaser, and then just before painting, wiped with a tack cloth.
Auto paint suppliers can mix the colour code for your bumper cover, and put it into a spray bomb, for less than $30 or so. Then just follow the directions on the can. Good Luck!