Yes, use a shortcode:
function aslums_first_shortcode( $atts, $content ) {
if ( IS INSIDE NETWORK? CHECK ) {
return 'inside the network'.$content;
}
return 'outside the network'.$content;
}
add_shortcode( 'aslums_shortcode', 'aslums_first_shortcode' );
In your post content:
You are: [aslums_shortcode]
As an aside, could a user outside your network bypass verification if they knew what the URL users inside the network are using? You may want to reconsider how authentication works on your network