You can add multiple accounts for the same exchange. There are two places you can do this.
On the Wallets page
On the Wallets page you can simply click on Add new exchange. In the pop-up that opens, you can then select the exchange you want to add, and a custom name for the account, and it will appear as a new account under that Exchange.
While inputting an transaction
- Manually - When you reach Step 3 - Exchange and Transfers you can type in the exchange name and select it by clicking or pressing Enter, and then when asked to select your account, you can simply start typing a new name and click on "Create..." or press Enter. A new account with the corresponding wallets will be created for you once the transaction is submitted.
- Through a CSV import - When entering a transaction on a line of the CSV file to import, you can simply input a different name for an Exchange Account, and this will be automatically created for you.