Change Vendor/Product Id of a USB Dongle
Full disclosure: this is purely speculation, worth a try but not intended to be the final word.

It would make sense that you can't change the VID/PID after the device is connected. Your idea of editing the kext may be along the right path, but from what I gather, OS X generally does not like to load modified drivers (because their signatures will no longer be correct.)

First, try disabling Gatekeeper (it's the option that stops you from running non-signed apps.) It's under Security &amp; Privacy in SysPrefs. 

If that doesn't work, this may be worth a try, but I don't know if it'll do anything. Some versions of OS X apparently have a switch that allows loading modified drivers (normally you can't). The command is:

sudo nvram boot-args="kext-dev-mode=1"


Then edit your kext, and rebuilt the kext cache:

sudo kextcache -m /System/Library/Caches/com.apple.kext.caches/Startup/Extensions.mkext /System/Library/Extensions


(Source: http://www.cindori.org/enabling-trim-on-os-x-yosemite/ - modifying kexts on the new OS X Beta causes them to fail to load, maybe this is still happening on older OS versions - it'd make sense, given Apple's strong security sense.)