How do you change a table's schema?

The cut-and-paste method described in another answer works well for tables with no foreign keys, and for a reasonable number of tables.

An alternative that preserves foreign keys is to export the model as a SQL script, edit it, and then import the new script into a new model.

Using MySQL Workbench v6.3:

1. File -> Export -> Forward Engineer SQL Script
2. Carefully edit SQL script. Replace references to one schema with the other, for the tables you want to move. Do this both for CREATE TABLE commands and foreign key references.
3. File -> New Model
4. File -> Import -> Reverse Engineer SQL Script

Unfortunately you will then need to recreate any diagrams. But that can be straightforward if you have the original diagram as reference (take a screenshot or export it to PNG or PDF.)

Use the model tab. You can cut out a table from one schema tab and insert it into another.