Yes, you are free to change your data mapping according to the business needs. So, after the demo migration is done, you will be able to see the newly created results of your mapping changes.
However, there is an option “Confirm Mapping for this module”. Ones you selected it and then pressed “Save All Changes” button, you won't be able to make changes in the confirmed modules by yourself.
It can be changed only from our side for your request by pressing “Unlock Request” Button.
Note: It’s not recommended to make any changes in your CRMs (e.g., add some custom fields for the saved modules, etc.) once you confirmed mapping for your Package (Customized Migration). It can adversely affect the successful migration process.
“Confirm Mapping” option is available only when the user is logged in.