You can install partial new GN4 version over an existing version.

IMPORTANT: test it on a copy of the production base, before doing it in production

Example for running i4 2.1 on database 2.0

On the 2.0 database upgrade the database using srv4 2.1 and the schema 2.0 of the customer.

In the appsettings.xml add this key:

<add key="Db.IgnoreVersion" value="true" />

After this you will have a 2.0 with the system tables upgraded to 2.1 but binaries still 2.0, and due to the key in appsettings.xml, the system will not complain about the different version.

Now you can install the I4 2.1 on the database 2.0.