most crystal calls are conditioned in a fairly small area, I would think over time you would condition a hole in the crystal?? Any problem with conditioning 3 more spots, say 3,6, and 9 o'clock?
Most well-made calls will be consistent around their entire circumference. Unless specified by the call maker there should be no reason you can't do what you are describing.
An example of the converse would be a shedua aluminum, i ( and many others ) have from Daybreak. Gary will tell you the sound he designed it for is best achieved by playing it in the areas where there are no holes in the back, It still sounds great in other areas, but not quite the same
The top left and bottom call have been hunting and getting scratched for 22 seasons now and still play great!
(https://i.imgur.com/bj20D1D.jpg)
The call maker usually conditions the surface to coincide with cuts in the sound board pedestal. He knows where the best sound comes from. That being said, there is no reason that you can't experiment and condition the whole surface. Only you know what the turkey in your head sounds like and you need to find that sound.