Microsoft is hard sealing the Dynamics 365 for Finance and Operations application suite as of version 8.0 (the Spring 2018 release), so customizations will now be done using extensions rather than overlays. This will make upgrades and implementations faster and easier, and lower the cost of code ownership. (You can learn more about the benefits of extensions vs. overlays in our recent post.)
Microsoft has released this schedule for the transition:
Creating Extensibility Requests
When transitioning code from overlays to extensions, you may come across objects that are not extensible. You then need to submit an extensibility request to Microsoft. Here's how to create a request quickly and easily in Lifecycle Services (LCS).
