Is there any way to keep the parameters of length, pan, vol of a sound that I tweak but then load a different sound in place?
I have GPO3 (Kontakt Player)
No, there isn't. Those edits you're doing are for the currently loaded instrument. As soon as you load a different instrument in that same slot, the new instrument's default values will load with it. But you can load up to 16 instruments per instance of Kontakt, if you have customized the player so all possible slots are visible.
It's highly recommended, thethomas, that you upgrade to GPO4 which uses the Garritan ARIA Player. The upgrade price for registered users is $50.