you will need to have DataAssist installed to make this change.
Once you have DataAssist installed, go to window -> server behaviors.
In the list of server behaviors, double click the Insert record server behavior. Select the column that the HTMLEditor content is being stored in.
the value section will show code similar to:
<?php echo((isset($_POST["country"]))?$_POST["country"]:"") ?>
the name of the form element will be different. edit that code to include the str_replace functions:
<?php echo((isset($_POST["country"]))?str_replace("<br>", "<br />", $_POST["country"]):"") ?>
don't change the name of the form element though.