Yes, and it does not change the price. A run of twenty polos can be any mix of XS to 4XL. Some garments carry a small surcharge above 2XL, which we show before you order.
The only place mixed sizing genuinely changes the maths is very small or very large sizes on decorated garments — a 4XL uses more fabric and sometimes a different print area. We flag that at quote stage rather than burying it in a surcharge you find out about on the invoice.
The questions are free. So is the quote.