I cannot use (clickable) HTML-forms in fields where I put a MIME transformation onto !

Due to a surrounding form-container (for multi-row delete checkboxes), no nested forms can be put inside the table where phpMyAdmin displays the results. You can, however, use any form inside of a table if keep the parent form-container with the target to tbl_row_delete.php and just put your own input-elements inside. If you use a custom submit input field, the form will submit itself to the displaying page again, where you can validate $_POST in a transformation. For a tutorial on how to effectively use transformations, see our Link section on the official phpMyAdmin-homepage.