How To Store Default Field Values And Warn Users When They Are Changed?

I have to add some technique which will solve the following problem. A form is presented to the user in our web application. Say it has

4 text fields,
2 radio buttons (Yes / No)
1 checkbox
1 select list.

Now 2 textfields are pre-populated, one radio button (Yes) is pre-selected, checkbox is not checked, one option from select list is preselected.

Problem:
In 90% of the cases, all that the user needs to do is enter values in the 2 empty textfields and click Submit.

However, the user might change the values in the preselected controls, like check the checkbox, change radio selection from Yes to No, select a different option from the select list, change the default values from the prepopulated text fields.

Now in such a case where 'default' values are changed, I need to show a alert or a popup layer to the user when the submit button is clicked.

Showing a popup layer or an alert:
The popup layer/alert will be a confirmation popup which will say something like -

"You have changed the default values for:[all the fields which were changed by user]. This requires you to do [some task] once you submit the form.

If you do not wish to change these defaults, click Cancel.
To proceed with the changes, click OK and then Submit."

Clicking OK:
If user clicks OK, then all is well. User will click Submit to submit the form and do some task which is required when defaults are changed.

Clicking Cancel:
If user clicks Cancel then the defaults should be restored. User is now free to click Submit. Code: