With enough time and resources, anything is possible. However, what you are asking for does not sound trivial. Generally the easier something is for the user, the more complex the tool is under the hood. The Roll20 framework, while based on HTML, CSS, and JavaScript, is proprietary. By the time you developed a visual editor you could probably have learned HTML, CSS, and JavaScript well enough to work with character sheets in a vastly shorter period of time. Also, you would already need to have these skills and a deep understanding of Roll20's framework to even begin on such an endeavor in the first place. To that end, I am not aware of anything in existence you could just pick up and run with. You may find some tools such as PUG or SCSS make character sheet creation easier. Scott C created a tutorial series to help new sheet authors develop these skills here .
