Will Pro Sites Affect Existing Blogs?

Hopefully a quick question...

Will activating and configuring Pro Sites affect existing manually created sites?

I have manually set up a few sites on our network for partners, enabling various plugins and themes for each. I now plan to deploy multiple levels of paid Pro Sites. Will doing so limit functionality or access to features on the current sites?

Just wondering if I will need to notify the current users and quickly extend Pro Site levels (or make manual tweaks) for them to keep plugins, themes, quotas etc.

Thanks!