Hey bud. This not my first bong rodeo. Please give me a little bit of credit for knowing how bongs work. Yes, you can pull just the bowl on some bongs. The stem and bowl are integrated on others. Then you have to buy an extra downstem and a bowl which jacks up the cost more.
Now, if you have a PROPER carb hole, then you don't have to buy extra stuff or pull the bowl. There is more to the carb hole than simply clearing the bong.
The carb hole also allows for actual carburetion during the hit. Such as mixing a little air by partially opening the carb hole while taking the hit. This optimizes the smoke to air ratio for the perfect hit every time! Good luck trying that by slightly pulling the bowl while you try to hit it. It's not happnin, Mon!