Forms personalizations are neat for doing simple things. But the functionality is limited/restricted. If you require more complex interaction and processing then its custom library.
There are also a few oversights in the Personalization functionality which i consider to be sloppy or lazy implementation. For instance...
... you can change field boiler-plate text, and alter LOV functionality, but you cannot rename the LOV title. So you could "modify" a form to rename certain fields to suit the client requirements (and replace the LOV code) but the moment they then click on the LOV you get the original field name/LOV name in the window. Sloppy. You cant get around this using personalizations, you can only do this using custom library.
... you want to disable the DFF block. Fine and dandy, but you are still left with the little [ ] graphic on the form where the DFF was!
However, if you also need the same processing to happen in the Self service pages then custom library obviously does not fully fit the bill, and you need to consider a more custom route...
Hey ho....I wonder if it gets any better in Fusion Apps