You can use Cheat Engine to find the memory address for your current balance and change it to any amount.
While in the game, press F1 to bring up a secret menu that allows you to give your agent money and manage other stats.
This is the most popular way to get rich. You must find an account with a high balance (often found during "Trace a Balance Transfer" missions), transfer the money to your own account, and then meticulously delete the transfer logs in both the target's statement and your own to avoid being caught.
