I realized that when you net send somebody, they can recieve a maximum of 6 messages. Is there any way to increase this number of maximum messages recievable?

It's more of a spamming filter than a limitation. However you can get around it by adding a delay to your program.

Here is a sample vbs program that I wrote to test this.
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Code Below
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Dim i, WinShell, ldate, lNumSeconds, lNumPrompts

'This delay is what allows you to send more than 6 prompts.
lNumSecondsDelay = 2
lNumPrompts = 20

Set WinShell = WScript.CreateObject("WScript.Shell")
ldate = now - 1
For i = 0 to lNumPrompts
while not now-ldate >= lNumSecondsDelay/(24*60*60)
wend
lDate = Now
WinShell.Run "net send ejohnson test"
Next
Set Winshell = Nothing