Will adding a parent category ruin my permaLink structure and Google indexing?

I currently have a category structure and permalink structure that is that is ranking well for longtailed results.

However I’m looking to add a parent categoryat the start of the hierarchy and I’m not sure the best way to do this and how it will affect my search rankings.

E.g.

Current structure:
URL/category/post title/post ID/

New structure
URL/category-parent/category/post title/post ID/

Whilst writing this post I thought perhaps I could use a tag for each of the categories then this way I would be able to develop an RSS feed with the tag in question???

The goal is to have an RSS feed widget on my homepage with two or three categories showing.

Thanks in advance
Lee