I have one AppExchange package, which is installed by various clients (for e.g. 100 customers).
One of these customers has a specific requirement and to complete that I need to create an unmanaged package with few reports/dashboards/process builder/Flows/Permission Set which will refer a few components (Mostly Objects, Fields) from my AppExchange managed package.
If you try to add a Managed metadata item (Object, Fields) into an Unmanaged package, it doesn't allow you directly.
But, if you try to add an Unmanaged Metadata Component (Reports, Dashboards, Report Type, Process Builder, Permission Set, etc.) which is referring a Managed metadata Component (Object, Fields, etc.), it adds Unmanaged metadata Components + Managed metadata Components (objects, fields).
With this behavior, I will be able to create an Unmanaged Package for one of the customers who have specific requirements.
But, I would like to confirm if this is a recommended way as per Salesforce 's Best Practice?