In accordance with the CRA regulations, your etax receipts are encrypted and cannot be changed once issued.

Instead:

1. You will have to 'manually' cancel the tax receipt number in your offline records according to your standard procedures as required by the CRA for audit purposes.
2. To issue a new tax receipt, use the Issue Single receipts section. In the accompanying email, make sure to include the tax receipt number of the original receipt; and a statement that this new receipt replaces the original receipt.
   • Tip: When creating the new receipt, you will see a line called "Fund Name". If you have enabled Fund Name in your Receipt setup (learn where), whatever you type in that box will appear on the new tax receipt itself. You can type something like "This replaces cancelled tax receipt # 12345".
3. You should also inform the donor that the previous tax receipt number has been cancelled, cannot be used for tax purposes and should be destroyed.

For further information about CRA regulations governing charitable tax receipts, visit their website:
https://www.canada.ca/en/services/taxes/charities.html