Since no one answered this is all that I’ve managed to achieve, maybe it serves anyone else stuck in this matter:
add_filter( 'um_first_name_form_edit_field', 'my_form_edit_field', 10, 2 );
function my_form_edit_field( $output, $mode ) {
$fields = UM()->builtin()->get_specific_fields( 'first_name' );
foreach ($fields as $key => $value) {
$fields['first_name']['placeholder'] = $fields['first_name']['title'];
$field_value = get_user_meta(um_user('ID'), $key, true) ? : '';
$output = '<div class="um-field um-field-'.$key.'" data-key="'.$key.'">
<div class="um-field-label">
<label for="'.$key.'">'.$fields['first_name']['title'].'</label>
<div class="um-clear"></div>
</div>
<div class="um-field-area">
<input class="um-form-field valid "
type="text" name="'.$key.'"
id="'.$key.'" value="'.$field_value.'"
placeholder="'.$fields['first_name']['title'].'"
data-validate="" data-key="'.$key.'">
</div>
</div>';
//echo $output;
}
return $output;
}
I still need a way to do this for all the fields not only for a specific one like this.
