Database Redesign
Changing cardinalities in a database is:

is impossible to do, so a new database must be constructed and the data moved into it.
a common database design task.
a rare database design task, but does occur.
a database design task that never occurs.

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Database Redesign
Before any changes to database structure are attempted one should first:

test any changes on a test database only.
All of these
create a complete backup of the operational database only.
clearly understand the current structure and contents of the database only.

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