If your project makes use of Webfiles, you should consider the following:
During the upgrade to CMS 12, all Webfiles will be reloaded. It is possible to reload webfiles on a running production environment, through the Hippo Console. While this is not a typical case, if you apply this practice for your project, you therefore have to consolidate any runtime webfile changes into the webfiles in your project sources, such that the subsequent upgrade will not revert your runtime changes unexpectedly.
For this, Bloomreach Experience Manager currently provides no tooling other than per-webfile downloading the content through the Hippo Console.
If your project's production system has no runtime-changed webfiles, no action is needed.