Oh man. If you can't do something like this I'm wondering why you have a signature that insinuates "hacker" let alone VB.NET/C# programmer.
Anyway, you wouldn't be able to manipulate fishing through these means. You're going to actually have to modify the SWF of the game and take other measures necessary.
Edit: Just a hint this also belongs in the Gaiaonline section.
Really? I seem to remember being able to set data values in .NET through the SWF object quite easily.