Object &1 type &2 already exists and will not be overwritten

What causes this issue?

Changes to existing domains or data elements will not be done
automatically by this generation module.
It's because domains and data elements may belong to other components
and are not application specific (e. g. CLIENT field, UUID types etc.).
Only new domains and data elements using the Z-prefix will be generated
and relevant fields will be added to structures and database tables.
Field setup changes in structures and database tables of course will be
done automatically.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

In case domains or data elements need to be changed (e. g. type or
length) a manual change is required using transaction SE11. This of
course may also cause manual adjustments in the relevant structures and
database tables.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.