Primary key type change not reflected in foreign keys with MySQL Workbench
Actually cascade updates for data types are not supported by Workbench.

One workaround, is to define User Data Types, use those in your tables, and if necessary, update the User Data Type. That will generate the correct DDL.

I usually create User Data Types for PrimaryKeys, Name, Description, Money, etc.

In your case will not work, as you should do that before creating the tables.
Now, if you must replace it in all your tables, do it for a User Type.

Other workaround for you will be to generate the database as is, go with the sugestion above, and then re-import the model to continue design.