DSpace 7 user interface's URLs are not customizable. However, all old-style 6.x Handles should redirect automatically in DSpace 7 to the new URL. So, an old style URL like [dspace.ui.url]/handle/[prefix]/[suffix] will automatically redirect to a new style URL like [dspace.ui.url]/items/[uuid].
In other words, while DSpace's new URL structure cannot be customized, all old URLs will still work to provide backwards compatibility with 5.x/6.x.