It’s a bad idea.

1. You should never flush rewrite rules on each request. That will hit the performance badly.

The last one is slightly better but still not recommend. why do you want to automate the permalink structure on theme activation?

It will take only 30 second to update it manually.

If you still want to do it, here is a cleaned version of your last one

function set_custom_permalinks() {

	if ( get_option( 'permalink_structure' ) ) {
		return;
	}

	global $wp_rewrite;
	// Save permalinks to a custom setting, force create of rules file
	$wp_rewrite->set_permalink_structure( '/%postname%/' );
	$wp_rewrite->flush_rules( true );
}

add_action( 'after_switch_theme', 'set_custom_permalinks' );

Regards
Brajesh

Hi Dianne,
I am sorry for the inconvenience.

Please allow us to put an update by day end Tuesday with the option to set it to None.

Regards
Brajesh

Hi Quint,
Thank you.

Probably you do not need to update that. The BP profile search plugin allows selecting mode when adding the field to search. Try switching the mode. They control the user Interface.

Regards
Brajesh

Hi Daniel,
I am sorry, I could not try the theme.

Will be doing so by day end tomorrow and updating you.

Regards
Brajesh

Hi Tosin,
Ravi is expected to work on it next week. Hopefully, we may have the update soon.

Regards
Brajesh