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If you are looking for my adivce i will suggest you to go without changing the hyphen and here are my reasons for that. Changing hyphen simply means changing the domain name for your website and redirection on the domain level always loose the link juice so your overall redirection from old domain to the new domain will loose the SEO power. Changing eCommerce platform is great but for that you should always keep in mind that the new platform have lots and lots of Seo plugins like the platform should allow the cahngings in robots.txt, indepandance on the xml sitemap level, titles, descriptions and more SEO related areas should be covered within the new platform. My point of view about your situation!