Fulcrum is flexible and allows you to make changes to your data collecting app, even during or after fieldwork. You can always add fields, as well as rearrange, edit, and even rename fields. Please keep in mind that if you modify values in a choice list, collected records will no longer contain the modified choice, nor will they contain the new values. Please note that if you delete a field, you will lose all of the data that field contained. Just like removing a column in Excel, what happens when removing a field in your app, is that it will remove the associated data.
In order to replace a field with a different field (e.g. switching from a choice list field to a text field) and the original field contains data, you must export the data before deleting the existing field. After the changes have been made you can import the data back by updating existing records and making sure that the column is mapped to the new field. This is because Fulcrum treats some data types very differently, and not all data can be re-cast between formats.