It has been always tricky to test Zoho Creator. What the system has prepared this time in point of data modification functionality?
You'll never know until you try.
To change the field type in Zoho Creator the user should enter table edit mode and select “Edit this field” option form popup menu:
After that you must choose the new type and save changes. Converting the field into “Choices”, Zoho Creator functions unassisted building up the list of database values.
This is how Zoho Creator resolves the issue, when the field value of the record can't be converted into the new type:
Zoho Creator offers good methods for data modification and it functions pretty well. But what would be also of a help for common users is gaining more control over mismatch between the old and new field type, just field with blank values is definately not enough.