he could be discussing maybe one of three "current" issues. one, if you are properly grounded. changing a head is like any other repair to electronics. just like changing memory, or anything else in a computer... latent static charge can zap the board. not having the printer ribbons seated properly and plugged into the proper locations after install. and most likely, each head has a "head rank voltage" (it's called many things). the heads have different sensitivities to voltage, which is what spits the ink out, so you input these numbers into the service menu for each head. i've personally never heard of it damaging a head (although there may be someone that can contest that). it has more to do with print performance. i've spoke with some techs that have said they've experimented with piezo printer head ranks and couldn't see the difference with the naked eye.
if you want to change heads, i'd look up a lot of info, photos, etc. and if you feel you can do it, go for it. techs are good for diagnosing shorts with motors, boards, and such, but changing heads is slowly becoming the job of the printer's owner.
