AC9 will run fine with AC12's dongle. I'm not sure if you have to customize the WIBU installation, try the below first.
You can't install AC9 from AC12's installation disks. You will have to get the AC9 disk from your reseller.
However, as David suggests, AC9's
installer
will not run on a Macintel. So you will have to install it on your PPC G4 and then copy the complete Archicad 9 folder to the Macintel. If you have already installed AC12 with WIBU support on it, AC9 should run fine as well, in PPC emulation (Rosetta) mode.
Besides, on the Mac, AC12's USB Wibu key will run all OSX-enabled Archicads, that is as far back as AC7.
AC4.1-AC26SWE; MacOS13.5.1; MP5,1+MBP16,1