Thank you for your reply.
I am glad to hear that you have managed to solve this issue. I will check whether our KB article needs to be updated further. The last link that did not work for you was to an help article which describes how to set a theme application at runtime when using .tssp files. You can navigate to this article by opening our help page >> Tools >> Visual Style Builder >> Working with Visual Style Builder >> Saving and Loading theme files.
I hope you find this information helpful. If you have any other questions, do not hesitate to open a new support ticket/forum thread.
All the best,
the Telerik team