"As far as I know" and "As far as I'm concerned"
I don't think it should be used as a replacement.
"As far as I know" would indicate that you have partial (i.e. not complete) knowledge of the matter being discussed.
"As far as I'm concerned" would indicate you're expressing your opinion about the matter being discussed.
They don't mean the same thing. "As far as I'm concerned" is roughly equivalent to "in my opinion" or "as it relates to me". "As far as I know" means what it says, something like "according to my knowledge".