Extensibility requests
Finance and Operations applications exclusively use extensions to customize the product.
We've been working toward an extension-based customization model for some time. Over the past several releases we have been gradually sealing models. As of Dynamics 365 for Finance and Operations release 8.0, this completes the sealing. From this release forward, only extension-based customizations are allowed.
In future releases, we will be adding even more extensibility capabilities to enable independent software vendors (ISVs) and value-added resellers (VARs) to deliver complete business solutions. We will prioritize these on a customer-by-customer basis with frequent releases.
Reference:
https://learn.microsoft.com/en-us/dynamics365/fin-ops-core/dev-itpro/extensibility/extensibility-requests