So you can't actually find anything that says the op can't replace his own anode then. Typical scaremongering from lying plumbers trying to drum up extra work for themselves.
You even have to try and criticise my grammar as you have nothing else to say. 'whom' is not a word used in Yorkshire. We're simple folk.
You know, it's times like this you miss dear old Dr Drivel, his objection to unvented cylinders was the stuff of legions!!
http://youtu.be/rDzC8RfJzJk
One of the many videos showing the results of DaftyDIYers or Electricians messing around with something they know nothing about.
Oh, here's another one, such fun!!
http://youtu.be/68p4ngS-yME