Switch Text to HTMLText on the fly
Assuming you have a model using plain scaffolding (like my simple team listing module for SilverStripe does) you can easily switch a $db field from Text to HTMLText in your config.yml, e.g.:
TeamMember: db: Description: HTMLText
You could also add new fields to a DataObject with that.
Running dev/build?flush we don't see anything (cause database doesn't need to change), but now we see automatically a HTMLEditorField scaffolded for this field.
Of course you cannot change order of the fields or do other fancy stuff withthis mehtod, but it's ok for simple, project specific changes.