Spoofing User Agent String

Hello AutoIt Community!

I'd like to ask for some help in spoofing the User Agent string so website('s) recognize it and act on what User agent they see.
Currently I'm developing a website that's about a Radio Stream.
I'd like to add a desktop client for it which loads the website.

For that I want the website to recognize the client and load another theme for that. The only way I know to script this is by checking the useragent and loading another theme for that.
I'm already that far that it loads up a Mobile theme if you browse with a Mobile Device

Now I'd like to spoof the User Agent that the website can see and load the designated theme for it.
I found some scripts via Google that redirects me to the autoit forums. But my knowledge about AutoIt is not at a certain point that allows me to embed this myself.

So therefor I'd like to ask the Auto It community for support!

Thank you all in advance!
Skorm