I am simply passing on a potential solution for mostly-answered threads in the read-only archived forums linked to here:
The best solution seems to be offered by FTDI themselves:
FT_INF 1.1 - Custom INF File Generator
FT_INF has been updated to be compatible with the latest certified version of FTDI's Windows driver, 2.08.02.
FT_INF is a free application allowing users to create custom inf files that can be used in conjunction with FTDI's proprietary drivers. Altering inf files gives users the flexibility to install FTDI devices that do not use FTDI's default Vendor ID / Product ID as well as fine tune some of the more advanced driver settings.
FT_INF is available for download as a zip file by clicking here. The full FT_INF User Guide is available after installation.
Please Note: FT_INF requires the Microsoft .NET Framework 2.0 installed on your system to run the application. This can be obtained from the Microsoft Website (http://www.microsoft.com/downloads/details.aspx?FamilyID=0856EACB-4362-4B0D-8EDD-AAB15C5E04F5&displaylang=en), if your system does not have .NET 2.0 installed please download the file from the above link. To install, double click on the dotnetfx.exe and follow the instructions in the wizard.
I stumbled across the archived forum entries when I was attempting to clone a company's "proprietary" USB to Serial cable, which really is an FTDI FT-232RL coupled with a Sipex high-speed TTL chip. Nothing fancy, but their software installs custom product IDs and vendor IDs using the above method, so I assume after having my prototype fail to match, and am planning on pursuing it as a solution.
Because of the open-ended nature of the last forum posts on the topic, I figured I'd share my findings here, just in case these gents are still wondering what to do. :)
It's great I use it heavily for some Sparkfun FTDI Serial -> USB interfaces that I use.
It can also be great fun when you give something as a gift, and Windows recognizes it with a custom name :)
Not wanting to hijack the thread, but I made a "Women's mood meter" for a woman at work who was very busy, and sometimes you never knew what kind of mood she'd be in at any given time.
So, with a few RGB LED's and a 16x2 LCD screen, the mood-meter was born. It basically allowed her to set her mood and show everyone from a distance via a basic VB.NET app. It was great when she plugged it in and saw Windows recognise it and display her name rather some random string!