That's fine and a good reason the team decided to do the dual process route rather than forcing people to update. Note however, new images will by default, come in with Process 2010 unless you go in and change your ACR/LR "Default" for your camera...
Without changing the camera defaults that someone else has gone to a lot of trouble to make, I was wondering if it is possible to sync the process engine settings across multiple photos, in other words, if I find that Process 2003 is better on the image, can I sync it across multiple images?
The only reason I ask is that in some cases it might be preferable to use the older 2003 process engine as it produces a different transition effect between colours and shades, thus avoiding some of the unexpected optical illusions. I have noticed, on the new process engine, that if you are not careful, you can bring in some additional problems, even with the default settings for sharpening. It is like the Rembrandt effect, that happens between the interaction of one shade and another, to create a third shade that is not really there. The 2010 Process, in certain photos using the default sharpening, produces an optical illusion of darker thinner lines around some objects with high contrast, but this is purely perception based on how the image is rendered. I have found that it may be necessary to reduce the sharpening to 1 and increase the masking to create smooth tones between transitions. This was not so much of a problem with the older process engine, but the transitions were rougher as a result.
After messing around a bit with the new controls I can see that it does produce some very good results. The reason I guess I had my initial unfavourable impressions was due to the fact that everything in the noise reduction and sharpening sliders, including moderate changes, had become a great deal more aggressive, thus causing some problems with perception of the end results.