Which bits do you not understand?
- On the entity form definition you can change the displayed label of the default button (Submit by default)
- You add JavaScript (jQuery) to the Entity Form in the spot provided that onchange of the Checkbox/dropdown changes the label on the button
- You add JavaScript to the Entity Form for when it loads to clear the Yes/No Dropdown
On the CDS/Dataverse side of things, you know when it was submitted as on create or update the checkbox is set Yes and you can use that to change the Status Reason (via a realtime workflow).
It is not clear from the detail you have provided, if there is a need to redirect to 2 different pages e.g. if you are coming off an Entity List then just redirect on submit/save to the List (use the Status Reason to stop people editing something that is Submitted). Other than the OnSuccess redirect, you can only redirect using JavaScript so what you can also do is OnSuccess redirect to Page X (passing the entity reference/id), and on Page X put some logic and use Javascript redirect to push to the page you want them on.
For this type of situation, you may find Web Form is a better construct to use, as each Step saves the record, on the last step you just put some text saying submitting this page is the actual submit (and attach a Metadata item to the last Step that changes the Status Reason to Submitted), and then append another button using jQuery that they can click to redirect somewhere else. - Hit Submit then the records Status Reason is updated, hit the other button redirect to another page (in both cases the data is saved).
