Is it possible in Illustrator to change the curve of two separate points at the same time so that the change is symmetrical? For example if I have a rounded cornered square but want to further adjust the top two curves, can I select both points and somehow pull the handle of one and have it adjust the curve of the other point at the same time so they remain equal?
If you select one corner of a shape with the direct selection tool, you can type the exact value you want in the contextual menu at the top of your screen. Just repeat this for your two top corners that you want identical.
comment: have you tried the anchor point tool (shift + C keys)? if you click and drag on a corner point it will pull out adjustment bars where the opposite curve point has the exact reverse direction and exact value of the one you are dragging.