I have a 6906 with the factory semi bobbed hammer. I few years ago, I picked up a new fully spurred hammer for it. Any tips or instructions on how to go about changing out the original hammer to the fully spurred hammer? Should this be only done by a gunsmith?

It's easy. Once you get the hammer and strut assembly out, drive out the strut pin (this will seem impossible till you whack it hard enough) and replace the hammer on the original strut. Return the hammer and strut to your pistol.
Let me ask you: why? You could still cock the hammer if needed, and lower it safely with the safety lever/decocker. So why the desire to change it? Most folks go the other way, and put a bobbed hammer on their pistol.

First take off the slide, and the take off the grips and free up the tension on the hammer stirrup.

When you pull out the Sideplate Assembly leave the small pin in (sear pin), the one that is held in place by the open forked end. (1 pin is part of the assembly). Use a small punch as close to the diameter of the hole as possible (they are different sizes) to push out the pin from the right side of the gun.

Leave the punch in, and then back it out just enough to pull out the Hammer, leaving the 2 levers to the right (firing pin safety lever and the sear release lever) captured by the punch. Try to do it with the gun on it's side. The Ejector/Magazine Depressor might fall out. Then replace the hammer, and thread the punch through the hammer hole, and then the Ejector/Magazine Depressor hole.

When everything is lined up, Push the captured pin in the Sideplate assembly through the hole, pushing out the punch while doing it, everything should remain lined up. Then snap the end over the cutout in the sear pin to retain the sear pin. Be careful as the Fork can easily bend or break. That will suck BIG TIME!

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Is it safe?