Hi PresPhuture,
Thank you for posting.
Yes, it is possible to control which category/tags are shown

/**
 * Filter the BuddyBlog form settings and limit category/tag inclusion.
 *
 * @param array $settings settings array.
 *
 * @return array
 */
function buddydev_filter_buddyblog_form_settings( $settings ) {

	$tax                        = isset( $settings['tax'] ) ? $settings['tax'] : array();
	$tax['category']['include'] = array( 1, 2, 3 );// category ids to include.
	$tax['post_tag']['include'] = array( 5, 7, 9 );// tag ids to include.

	$settings['tax'] = $tax;

	return $settings;
}

add_filter( 'buddyblog_post_form_settings', 'buddydev_filter_buddyblog_form_settings' );

Please change the ids with your own. It will only list the category tags with those ids. I hope you can modify it form there on.

Hope that helps.

Regards
Brajesh

Hi PresPhuture,
I will check it on a demo and let you know today. I am not sure what is wrong with the above code.

Regards
Brajesh