I've done the opposite, gone from a 17 pin CRT to 25 pin LCD, put the process is the same. You have to swap out the monitor shelf and the wiring harness attached to it that goes to the motherboard. You have to change the shelf because the 17 pin & 25 pin connectors are different sizes and the mounting holes on the shelves are different for each.
They added some pins for separate grounds on the RGB signals, added pins for a serial EEPROM in the monitor, and a couple of other things. The motherboard side of the cable is the same for a 17 or 25 pin cable though, so I'm not sure why they changed them. I attached a couple of drawings showing the monitor side pinouts (P340) so you can see the differences.
I have a 17 pin monitor shelf for a 17" cabinet that I've been looking to swap out for a 25 pin shelf. Let me know if you're interested in a trade.