Lots of possible adjustments on a variety of different style carbs. In addition to a high and low mixture screws. A carb may have an idle speed adjustment, a high speed limit screw to control max RPM as well as governor adjustment to maintain engine operating speed in industrial type applications.
Throttle control, choke adjustment, float level adjustment(which may be a tuning adjustment).
Needle position adjustment (also a tuning adjustment). Found on most slide type carbs. But typically not on CV slide carbs.
Depends on the carburetor type and emission control requirements. For example for decades Briggs diaphragm carburetors had a low speed mixture adjustment. Other carbs although nearly identical to there older counterparts have epoxied screws, and or limiters to prevent that particular adjustment.
In summary not all carbs have all adjustment, some maybe be modified to make them adjustable, if only partially.
Adjusting and tuning, closely related. Tweaking adjustments and or replacing jets and other parts to achieve the most power while avoiding engine destruction.
If tuning interests you, there are publications available to help you learn. Here's a couple. Even though they address slide type carbs, the priciples are the same.
http://www.briggsracing.com/sites/default/files/carburetortuningguide_ms10429_0.pdf
http://www.sudco.com/jetting_assistance.html
