Use Regedt32 to navigate to:
HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows NTCurrentVersionPorts
On the Edit menu, Add Value name as a type REG_SZ.
is the actual port such as LPT1: or COM3:.
In the String Editor, enter the correct value data.
NOTE: LPTx ports have a blank string.
NOTE: COMx ports have BaudRate,Parity,DataBits,StopBits,FlowControl where:
BaudRate=75,110,134,150,300,600,1200,1800,2400,4800,7200,9600,14400,19200,38400,57600, or 115,200
Parity=n,o,e,m, or s
DataBits=4,5,6,7, or 8
StopBits=1,1.5, or 2
FlowControl=not entered for none, p for hardware, or x for XON/XOFF.