It all depends on how the server interprets your packet.
Packet editing requires some logic, and some knowledge on how it works.
But put simply. If you send to the server that you had 10 million silver, that's basically you telling it how much you have, doesn't mean it will believe you, as the server already knows how much you have. Some packets are [ack] packet or confirmation packets, some packets are [syn] packets, or synchronizing packets, some packets are just plain [data] packets or information packets. The server really ultimately decides what to do with the packets you send it. Servers tend to have rules for each packet type, and what they enforce upon them. The best way to find out what the server does with each packet is to do Trial-and-Error.
I personally say, if your going to packet edit, test it with a throw away character, since if you send a malformed packet, and keep doing so, CO may interpret you as a bot, and send you to Bot Jail, or just Ban the account.
btw, no, if you sent the server you had 10m in cash, you will not recieve 10m in cash.