How can I dynamically add/remove tag in web.config in asp.net 2.0 from a code-behind file of an aspx page?

Pebble asked: I am developing a website where it is required to dynamically change the theme of the site chosen by the end-user. I have found that changing the “Page” tag’s theme attribute controls the theme of the whole site. But can anybody tell me how can I do this when a user clicks on [...]