Need to convert some characters

Hello
I try to find how to do it but i don`t find anything to make it work.

So.. i need to convert some characters when i publish something.

For example:

I write: ][‘;’-
and theese characters need to be converted in letter i need when is inserted to database.

i need: “\” to be “a” , “]” to be “t”

thansk for the help.