Populating form fields with DoQuery results

What I understand from your description is that:

1. you are creating a new record or editing an existing record
2. next, you want a button on the form the will take various values sitting in the open form and make an API_DoQuery request
3. finally, you want to take the response of the API_DoQuery call and parse the results and stuff them into some other field on the open form

This is easy to do with script but there are two issues. (1) To the extent that the values sitting the open form are used in forming the API_DoQuery it is possible that these values may be changed by the user after the API_DoQuery returns a result. This may create an inconsistent state as the results of the API_DoQuery do not reflect the values of the fields that were changed. (2) Likewise, I suppose it is possible for the user to modify the field that received the parsed results of the API_DoQuery if they make their change after the button is pressed. Again when the form is saved it is possible that it may reflect inconsistent or state information.

Other than that this is easy to do with script once the details of the fields and query are supplied.