We actually went through this process and found that it can be done but I'm not sure I would recommend it. Our Portal is in a "lite-production" phase so there isn't a lot of content but we had enough that I wanted to try this route. We used scripts to update non-hosted service URLs and web map layer URLs, but for some reason we missed some content and I ended up using ago-assistant to fix those manually. We also had a few hosted feature services that will need to be recreated and related/dependent content updated.
The one unexpected issue was related to Insights. Insights stores all its pages and workbooks in Hosted WorkSpaces. Fortunately, all of our Insights work has been test related so it was acceptable to let those go. I also found that I couldn't delete any orphaned Insights WorkSpaces in the Federated Server's Home > services > Hosted Admin page (I could do this for Hosted Feature Services). I received a: 'Failed to create data source ''/enterpriseDatabases/AGSDataStore_ds_w7oh234m''' message and the WorkSpace remains listed in the Hosted Folder. This may be related to the fact that we also reinstalled DataStore (long story). However we were able to delete the broken Feature Services that had pointed to the prior instance of DataStore. For now I'll just ignore them.
It was also necessary to update the serverURL in <configstore>\security\security-config.json. That file retained the prior web adapter URL. Without this change Insights wouldn't work properly. I'm hoping this change wont have repercussions.