When it comes to the validations these are on the page toward the top, the validations start with this line:
$WAFV_Errors = "";
You can remove any of the validations here for any of the form elements you do not want validated. Once you have removed the validations for the field you can modify that field without any other effects.
You will also need to remove the spry validations, toward the bottom of the page you can find the spry validations, you will need to get rid of the validation for the field, the find the spry message near that form element and get rid of it, the message should be in a span tag that has a class that ends in RequiredMsg.
If you are interested in putting new validations on the page you will need to make use of the Validation Toolkit but it is not needed to remove the current validations.