Yes, you can update the hsn code in item master during voucher entry in BUSY by follow these steps:
Step 1: Go to transaction section then click on required voucher type like sales, purchase etc.
Step 2: Click on add then specify the voucher series, date, number, sales type, party name and material center in heading.
Step 3: Now, select the item then press alt+m at item master to open the master in modify mode.
Step 4: Update the hsn in item master and save it.
Step 5: Afterward, specify the item with quantity and price then apply tax and save the voucher.