I agree with most here: If it's your knife, you are free to do whatever the hell you want with it, just be sure to disclose what you did if/when you sell it. That's only fair.
I don't agree with people who think that using anything other than the CRK grease is "modifying" the knife though, as that's just silly. I've used several different types of oils and lubes to try and get what I feel (and yes you can feel a difference) is the smoothest action from the stock knife. The good news is that the CRK grease is in the top 2 of all that I have ever tried.
My current recipe is this:
Use a very small amount of the CRK grease on the blade only, applied with a small detail paint brush. You are not globbing this stuff on, just trying to apply a light, even coat to the blade. Then, I put a single drop of Diaiwa reel oil on my finger and work it into the washers, only on the side that touches the blade, and then reassemble.
I'm not sure why, but this combination seems to both add another level of smooth to the action, as well as keeping it smooth longer than by using grease alone.
One final thing to remember is this: Doing ANYTHING to the knife *may* affect the resale value of it, including just sharpening it, so be aware of that. If you are going to use the knife like the tool it's intended to be, than I'm sure most won't care. If you are a collector, leaving the knife absolutely stock- factory edge and all, is always (yes always) going to be your best bet.