It's not something I've had to do, but KB P26983 details the 4GL approach, but personally I would try and hook into the Data Dictionary's own routines, that way you are following Progress' own procedures. [Edit] Also directly altering the _File... tables is something I would avoid if at all possible, as they are really meant as a reporting resource, and schema updates should be carried out where possible using Progress tools and routines.
I suspect you will have to upgrade to v10 also, as this will allow online schema changes.