Multiple excel formulas

Ok, so I am first using the following formula to get my account string: =IF(H20>=400,"8"&RIGHT(S20,4),S20). This turns my account number from a 78899 into a 88899. Unfortunately that account doesn't exist. The 78899 is a default number that needs to be changed to a 88000 or a 88010 depending on the description in another column of excel. How do I maintain the original formula (because that formula works to change account numbers that already in a 78010 format that gets changed to a 88010 format. I need the first formula to also be connected with a secondary formula to look up key words in a field, i.e. pizza, or airline to then change the 88899 to a 88000 or 88010.