you need to set the printer id per copy
the filter looks like this

$printerid = apply_filters('wppizza_gcp_filter_copies', $printerid, $cp);
where $printerid is – obviously – the printer id and $cp is a simple count depending on how many copies you have set to print

you are supposed to USE the filter in your theme’s (or actually your child theme’s) functions.php file , not replace it. that defeats the point of having filters in there in the first place

in short, you need to put something like this in your functions.php

function myprefix_wppizza_gcp_filter_copies( $printerid, $cp ) {
if($cp == 1){
return 'some other printer id'; 
}else{
return $printerid;
}
}
add_filter( 'wppizza_gcp_filter_copies', 'myprefix_wppizza_gcp_filter_copies'. 10, 2 );