Pattern search and replacement in shell

I am helping to set up a production AIX UNIX box in my shop. We have several SAS scripts that will be running monthly and will need monthly changes to their code. The SAS code is in the form of a text file, so I think we will be able to accomplishthese changes using a shell script. I know I can locate the patterns that need changing using awk, but I have not come across anything that will replace them for me once found. There must be a way, and I’m sure it’s not difficult. 200 easy tech points to anyone who can set me up with a solution. -Thanks