Use this function to change the user role names in BBPres

BBPress Custom Role Names

function bbpress_custom_roles() {
	return array(
		bbp_get_keymaster_role() => array(// Keymaster
			'name'         => 'Custom Keymaster Role Name',
			'capabilities' => bbp_get_caps_for_role( bbp_get_keymaster_role() )
		),
		// Moderator
		bbp_get_moderator_role() => array(
			'name'         => 'Custom Moderator Role Name',
			'capabilities' => bbp_get_caps_for_role( bbp_get_moderator_role() )
		),
		// Participant
		bbp_get_participant_role() => array(
			'name'         => 'Custom Participant Role Name',
			'capabilities' => bbp_get_caps_for_role( bbp_get_participant_role() )
		),
		// Spectator
		bbp_get_spectator_role() => array(
			'name'         => 'Custom Spectator Name',
			'capabilities' => bbp_get_caps_for_role( bbp_get_spectator_role() )
		),
		// Blocked
		bbp_get_blocked_role() => array(
			'name'         => 'Custom Blocked Role Name',
			'capabilities' => bbp_get_caps_for_role( bbp_get_blocked_role() )
		)
	);
}
add_filter('bbp_get_dynamic_roles','bbpress_custom_roles');