SQL Server service account change from virtual account to AD account
The virtual accounts tied to the service sid (in this case NT SERVICE\MSSQLSERVER) will retain any permissions given to them. This is because they don't go away, they are still tied to the service via the service sid.

When you change the account, for the example you gave, other than a few house keeping items there is nothing else given. It is very well possible to change to a domain account that does not have the proper permissions to even start the SQL Server service. Nothing is transferred.

For example, if you had an account that had full access to read and write to a directory not in the SQL Server standard locations (that are part of the install process) and changed the account, the permissions stay with that account. The new account would need to be granted those permissions in order for SQL Server to properly work with anything in that folder.

The last part of being linked to the virtual account. No, they are not linked. The virtual account and service sid will stay with whatever they had.