replacement on post level

[2hero]

I need something like replacement variables, but that will work modity post message only, not generated by forum HTML code.
I wanted on my board to modify some spelling mistakes and to put wrong letters in <font color="red"> </font> tag. But when i did this, post preview on threads list is broken now and above thread title apears part of 1st post beginning from first change, and that's because of "" in my replacement. Ofcousrse i could use color without "", but there are some other replacements, that i wish to make, and that i don't want to modify part of webpage.