Replace default Bulk Actions option name by overriding bulk_action method of WP_List_Table

custom-list.php

protected function bulk_actions( $which ) {
	if( $which == 'top' || 'bottom' == $which ) {
	?>
		<div class="alignleft actions bulkactions">
			<label class="screen-reader-text" for="bulk-action-selector-top">Select bulk action</label>
			<select id="bulk-action-selector-top" name="action">
				<option value="-1">Default option</option>
				<option value="1">Option 1</option>
				<option value="2">Option 2</option>
			</select>
			<input type="submit" value="Apply" class="button action" id="doaction">
		</div>
	<?php
	}
}