I would agree that you probably won't damage anything. however some cards just don't like it and won't function properly at lower than 33 mhz speeds. if you aren't having any problems then you should be fine.
Only reason I asked was cause I was getting a clicking sound for my HDD. This only happen when I tried to make a movie using the software that came with XP home but after I updated it that clicking stopped. As soon as I can unlock it I will be upping it to 166 MHz that way the PCI and AGP are in specs.