Can we use "As far as I'm concerned" in place of "As far as I know"? Or, are there some specific scenarios where in we do not have to use one in place of the other phrase?
Both of them can't be as a replacements.
"As far as I'm concerned" : is when you feel to express the limit to which you really bother about a situation. Beyond that valid parameter actually you don't care to pay heed even if you know something.
Eg: As far as I'm concerned, my job for this module is done and anything extra would be done only after a long thought process.
"As far as I know" : is when you feel to express the extent till which you are aware or knowledgeable about the entity.
Eg: As far as I know, winters in North India are terribly cold and would range between 0 degrees to 2 degrees centigrade.