2 quick thoughts:
1) I am not sure that deleting the field deletes the database field. I tried it once and was able to create the same field on top of the old one preserving the data. I cannot tell you now which version or field types. Try it out in a test workspace or test server.
2) You could also rename the field and create a new field, and write an update query to populate the new field from the old one. This would be much cleaner than editing schema files.
Let me know if you need any help on either.
Considering you're on a version which has the Form Designer, there are several more locations then just the schema file where this information is listed. The primary one I can think of is the FBDesignData.json file which holds the data for what the form looks like. When you rename this file it will be recreated from the other sources, that tell it how the form should look, when you open up the Form Designer.