You will not lose it necessarily, but it will change for sure... search engines surely notice that your site changed and rate it again based on the new information. However in fact, your website is constantly rated, since modern search engines consider also changes on other sites linking to yours for example (it is a complex rating network and no one really can say how a particular search engine works - otherwise it could be abused to push certain sites).

Anyway, I don't think that there will be a high impact on your site's rating. But cannot say this for sure (who can ?).

All in all if you feel that it could be an issue with the shop URLs (but I think more to customers having bookmarked such URLs), you may consider implementing URL redirections from the old URL schemes to the new ones.