[@macpresss Participant 12 years, 9 months ago]

Finally after 2 years I got a result to give each forum it’s own template!

<?php if ( is_single( array( 52, 89 ) ) ) {

	bbp_get_template_part( 'some-template' );
}
else {

	bbp_get_template_part( 'some-other-template' );
}
?>

Very simple..