Dean,
I am not entirely sure that this KnowledgeBase is still valid for recent versions of NI-VISA. What version of NI-VISA are you using? Here is what happens with NI-VISA 3.2:
ASRL10 is reserved for the parallel port, but it is mapped to LPT1
If you have more than 9 serial ports they can still be mapped to COM10, COM11..., however they may be shifted for example ASRL11 is mapped to COM10.
It seems you would only need to modify VisaConf.ini if you are using ASRL1, ASRL2... and need ASRL10 to be a serial port. Is this your case?
If you have to replace VisaConf.ini you can automate this by building a separate application that does this task. I've attached a VI and EXE that does this so you can see an example. If you run the executable in a folder that contains your VisaConf.ini file it will replace the original. You may want to have the front panel close when finished so the user doesn't see anything but this is just an example.
You can also include the this executable in your installer and in the Advanced options choose Run Executable After to have the installer run this program and your end user will never know it happened. Remember that you end user will have to have an identical system, or you should not replace the VisaConf.ini!
Shawn B.
National Instruments