First, check backwards compatibility of the old mapping impl (through the adapter);
Then create a new URI mapping implementation from info.magnolia.virtualuri.VirtualUriMapping, to replace SiteMapVirtualUriMapping

• https://git.magnolia-cms.com/projects/MODULES/repos/google-sitemap/browse/src/main/java/info/magnolia/module/googlesitemap/config/SiteMapVirtualUriMapping.java#61,85
• Use upgrade task to update old virtual mapping to new mapping also