First of all, this is a minor thread about the paid service "race change".
When you race change, your home faction rep switches with your new race home rep.
For example, if you change race from Blood Elf to Tauren, the Silvermoon City reputation will switch with you Thunder Bluff reputation. However if you were exalted, both your old main faction and your new main faction will count towards ambassador.
WoWScrnShot_012811_184108.jpg picture by aramourn1 - Photobucket
Besides that, there is some funny bug when you Faction change.
If you change race to Tauren, your spawn spot will be outside. Now, before you Faction change, go sit on some very Alliance-like mount. You will still be on that mount when you log in as a Tauren. But remember, when you dismount, it will be gone forever.
I hope this is useful in some way to you.
Edit:
Realized I should have named the thread differently, sorry if you opened this expecting something different.