It seems that you have opened a forum and support thread on the same issue. I will post the answer from the ticket here as well but if you have any comments on it, please, write them in the support ticket, so that we avoid duplicate posts on that matter.
What you are trying to achieve with the CSS prefixes would require a lot of customizations (including client scripting) and may not be worth the efforts having in mind that any possible clashes in the CSS could easily be fixed using only CSS (selectors with higher specificity). Furthermore, we could not give you working code and instructions for your specific scenario without having a runnable proejct to work on, as this depends on the site implementation.
That is why I would suggest that you only change the Skin name and do not change the control name in the CSS selectors. This way you could also easily make the SkinManager work with your custom skin. Instructions on using custom skins with RadSkinManager are provided in this article:
Then, if you encounter styles from the base stylesheet overwriting styles from the custom skin, you could simply increase the specificity of the respective selector in the skin file or in an external stylesheet.
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