change com port number to specific number

Question

I am having RFID reader when it installs in system it shows me com port 17

but when i run the application it doesn't work..

when i change the com port to com 3 from device manager properties, It works properly..

i think com 3 is hard coded in api...

I don't want to let the client to change com port from device manager, 

is there any provision to change com port from c# code..

 if yes plz help me...

Thanx in advance