Example of how to override the SPCO.calculate_target_attendee_input_id method so that you can exclude specific inputs from being copied.

tw_ee_exclude_inputs_from_spco_copy_function.php

<?php //Please do not include the opening PHP tag if you already have one

// This function allows you to set inputs to be skipped during the copy attendee info function shown on SPCO.
// It currently skips the 'fname', 'lname', 'email' questions but you can add your own input ID's to the exclude_array.
function tw_ee_exclude_inputs_from_spco_copy_function() {
    wp_add_inline_script( 
        'single_page_checkout',
        "jQuery( document ).ready(function($) {
	        SPCO.calculate_target_attendee_input_id = function ( primary_reg_input, targeted_attendee) {
				var new_input_id = '';
				// here we go again...
				var input_id = jQuery(primary_reg_input).attr('id');
				//SPCO.console_log( 'calculate_target_attendee_input_id : input_id', input_id, true );

				if ( typeof input_id !== 'undefined' ) {
					// split the above var
					var input_id_array =  input_id.split('-');
					//SPCO.console_log( 'calculate_target_attendee_input_id : input_id_array', input_id_array, false );
					// grab the current input's details
					var qstn_base = input_id_array[0];
					//var reg_id = input_id_array[1];
					var input_name = input_id_array[2];
					var answer_id = input_id_array[3];
					// var input_value = $(this).eeInputValue();
					// SPCO.console_log( 'calculate_target_attendee_input_id : input_name', input_name, false );
					// Setup input exclusions array
					var exclude_array = [ 
						'fname', 
						'lname', 
						'email'
					];
					// Check if the primary reg input id is in the array, if so, skip it by not returning an input ID
					if( exclude_array.indexOf(input_name) > -1 ) {
						//SPCO.console_log( 'calculate_target_attendee_input_id : input_name', input_name, false );
						return '';
			        }
					new_input_id = '#' + qstn_base + '-' + targeted_attendee + '-' +  input_name;
					if ( typeof answer_id !== 'undefined' ) {
						new_input_id = new_input_id + '-' + answer_id;
					}
					//SPCO.console_log( 'calculate_target_attendee_input_id : new_input_id', new_input_id, false );
				}
				return new_input_id;
			}
		});"
    );
}
add_action( 'wp_enqueue_scripts', 'tw_ee_exclude_inputs_from_spco_copy_function', 11 );