Will seach engine ranking be lost if I installed Ceon URI Mapping (SEO) now?

I have been running my shop for a year now, and for most of my keywords I am ranked very very highly in all search engines.

If I install Ceon URI Mapping (SEO) now, will i lose that ranking?

(my concern is since ranking in connected to the site's url, and installing Ceon URI Mapping (SEO) will change those urls. )

thoughts/ advice?

You don't really need any kind of URL re-writing anymore. There are a few minor advantages to using Conor's module - none of which have any influence on SERPS - but the search engines now prefer that URL re-writing is NOT done on dynamic content sites.

Matt Cutts (Head of Google search Quality Control) has been saying now (for many years), that URL-re-writing can actually do more harm than good.

(Conor's mod, however, is one of the more reliable URL-re-writers, so will not do any "technical" damage... but you don't really need to install it...)

Don't even bother with this. Leave the site as it is (technically) and focus on doing good SEO work in the "conventional" manner.