How does a business add an emoticon for mobile notifications after a transaction?

[lumisota]

From a while back:

Monzo Insider Ep1 - Instant Spending Notifications

@anon44204028 guessed correctly the initial automated system takes the “merchant category code” (MCC) we receive from MasterCard and maps this onto one of our categories. After this we may change a merchant if it’s been incorrectly assigned, but I think that’s relatively rare.