Forums Scripts & Popups $replace()

I made a theme, and everything i type is put to a %var befor it sends to the channel, how would i the simplest way replace words in the %var ? lets say it is: "%var I will bb" then i want bb to be replaced with be back .. or if i type "i will bbl, see you soon", then bbl should be replaced with be back later, i solved it if it's stored as firts input in the %var, but not if it's in the middle or if it's in the end of the %var .. i did try to solve it true the mirc.hlp, but couldent.. any ideas?

;--------- Edit

Every word that would be replaced are stored in a txt file..

Pseudocode:variable = $replace(variable,original text,new text)
Use $replacecs if you need a case sensitive version
$replaceex to restrict the replacement to strings that haven't been changed (this is handy if the original text is in the new text)
$replaceexcs: case sensitive version of $replaceex

You might also do a search for an Acro or Acronym script..I know they've been done a lot on various sites.