I managed to look into this for you. Thing is, you CAN change them. Actually, it's quite easy.
Each class is 0x63 (or 99) bytes in size.
The very first byte determines if the class is active or not. Set it to 0 and the default class is used. Set it to 1 and the information following is used.
Or something like that. I was using ReClass just now on it....But then I knocked my laptop and fked up the hard disk so I lost it....