Thank you for your reply.
The main reason you cannot achieve your task using themes is that themes can be applied to RadControls and not to elements. In the cell formatting event you have the cell element and this is why you have to use code. Basically what you can achieve through VSB you can achieve through code, after all the repositories you create in VSB are translated to code so they can be applied. You can again create objects to hold the settings and use them in code the same way you use repositories in VSB.
I hope this clarifies the situation. If you have further questions, I would be glad to help.
All the best,
the Telerik team