Changing an info site into an e-commerce? Effects on SEO?

If I have an existing amazon affiliate infosite talking about the types of iphone cases [iphonecase.com] and completely change it into a e-commerce site [iphonecase.com] with a blog [iphonecase.com/blog] selling iphone cases.

Will I lose a lot of the ranking i gained from the long tail keywords [iphonecase.com/top5iphonecases] > redirects to [iphonecase.com/store] even though the e-commerce site is relevant to the niche? These redirects will all have to be 301s?

What if I open a new domain and host all the old existing amazon affilaite information [iphoneloverinfo.com] ? and I link everything from the new domain info pointing to the new ecommerce site [iphonecase.com]?

Why would you want to change your perfectly good and already ranking content?

iphonecase.com/top5iphonecases should be just that, a page about the 5 best iphone cases, only now you are selling your own cases, not amazon's. And it should also be linking to iphonecase.com/store. But no redirection. If anything you should reporpuse your content.

I want to change it because I want the branded url of [iphonecase] the infosite as the brand of my ecommerce store.

The trademark and brand of the info site works better for my ecommerce store in my case.

bump?