Shamim's Plugins

Sorry for late reply.
You can add following code in your theme’s (child theme’s if you are using) functions.php

add_filter( 'gettext', function( $translated_text, $text, $domain ){
    if ( 'front-end-pm' == $domain && 'Toggle Messages' == $text ){
        $translated_text = 'Expand';
    }
    return $translated_text;
}, 20, 3 );

There are lots of changes. It is almost a new plugin now. Please see changelog bottom of https://www.shamimsplugins.com/products/front-end-pm-pro/

It will be better if you can update and then work on new template files. Please backup full website (files and database) then update.

It depends on so many things.
better you can update in your staging website, then test. if everything works then update in production website.

Let me know if you need any assistance from me.

Please follow https://www.shamimsplugins.com/docs/front-end-pm-pro/troubleshoot/license-keys-not-activating/

Let me know.

Also please note that, license does not restrict any functionality of the plugin. So user registration will not have any impact for license. Main purpose of the license is to deliver update and support.

I did not tested this plugin with Flatsome theme. Also all supported forms are listed in plugin settings page as well as plugin description. Flatsome is not listed there.
You can send me that theme so that i can try if i can fix it.
Or, you can contact me through https://www.shamimsplugins.com/contact-us/ for a refund.

It is possible but need custom coding.
You can contact through https://www.shamimsplugins.com/hire/

You can use condition inside that function.

add_filter( 'fep_filter_message_before_send', function( $message ) {
    if ( get_user_meta( get_current_user_id(), 'privacytel', true ) != 'No') {
	    // The @ symbol must be surrounded by character on both sides
	    $message['message_content'] = preg_replace( '/[^@\s]*@[^@\s]*\.[^@\s]*/', '[EMAILNASCOSTA]', $message['message_content'] ); # for emails
	
	    // Take any string that contains only numbers, spaces and dashes,
	    // Can optionally have a + before it.
	    $message['message_content'] = preg_replace( '/\+?[0-9\-]{5,}/', '[TELEFONONASCOSTO]', $message['message_content'] ); # for phone numbers
    }
    return $message;
});

Instead of fep_get_the_id() use $message_id