Flexfield Validation

 Is there anyway to setup a type of validation on data typed into a flexfield that would cause another entry?  Hmmm, let me give an example:

Let's say there are 4 vendor code flexfields.  I enter some text ('M&O') into vendor code flexfield #1, a validation rule kicks off that checks it, the code is M&O so it places the text 'Contractor' into vendor code flexfield #2, OR it checks the small business flag, OR both. 

We're limited as to what kind of customizations we're allowed to do so I'm hoping there is a validation feature that we can use to do something close to this.