Great topic Bulldog!
I've replaced the pickguards on both my Gibson J-60 and my Collings. It's not that bad and actually kinda fun.
To start with, a clean removal is key. Heat the pickguard with your wife's hair dryer and use something to start the peeling off process. I used a thin teflon coated spatula but I've heard of people using fishing line, putty knifes or gasket scrapers (the latter I would not recommend). If it's too sharp, you could gouge into your finish. Heat it up just enough to get the glue to liquify and it will peel right off. DO NOT OVERHEAT or it will cause your finish to blister. This is why I recommend a hairdryer. A heat gun is ok but will get hotter faster, so be careful. Today's nitro-cellulose finishes are extremely tough and it will take more heat to ruin the finish than it will to get the glue loosened up.
After you get the old pickguard off, then you have to clean off the glue and residue. You'll want to use Naptha for this process. I used Ace Hardware VM&P Pure Naptha. It won't hurt the finish but it will take a while to get all the glue off. Use a soft rag or an old T-shirt keeping it wet with the Naptha. Again, it will be time consuming and you will probably need to scrape some with your thumb nails. Be careful not to go crazy and get into the finish.
All of that was the hard part. Now depending on what you install you may want to buy material and make your own. This is what I did on the Gibson. It had to be either exactly the same size or oversized because my Gibson is older and had a significant "tan" line. So I got some material from LMI and traced it and cut it out. This was my first experience and I broke a piece off while cutting it out. You must put it in hot water and keep it hot while cutting or else it will break. Well my Gibson is full of checking and finish cracks and even a bad top crack, so I just went with it and installed it anyway. After I finished cutting, sanding and beveling the edges, I put the two pieces together on my adhesive sheet and it turned out great. The broken off piece flows with the rest and it looks like a fine hairline crack.
The Collings was an aftermarket pickguard already cut. It did not match up in size but that's ok. The Collings was new enough to not have a tan line. You can barely see where the old pickgaurd was but only if you hold it at a certain angle in just the right light.
Before you install the new pickguard, clean the top with Windex or some other cleaner that will remove the Naptha residue and any oils from your fingers. Next, lay the pickguard exactly where you want it. Study this and take your time. Nothing worse than getting it on crooked or not lined up with the soundhole rosette after all this work. When you get it where you want it, Tape the outer edge of the pickguard to the top and check again to make sure it's still in the right place. This will create a hinge. You should be able to lift off the soundhole edge and open it like a book. when you "close the book", it should fall right back into place. Now it's for real, open the book, peel off the backing on the adhesive sheet and slowly and gently lay the pickguard back down working from one end to the other. Don't slam it down all at once.
I wanted to talk more about making a bevel, installing the adhesive sheet and polishing but this is already too long. Someone else can jump in and may have some better ideas. I'll post some pics later.