You can't modify submitted entry data??

I’m trying to write an EE2 extension that modifies entry data before it’s inserted into the DB.

I’ve been working with the Channel Entries API Extension Hooks which work pretty well in providing access to the data. Problem is I don’t see how I can pass my changes back for insert/update. According to the documentation there are no return values available.

Am I correct in thinking that the only way to accomplish this right now is to do some sort of convoluted update after insert process or take over the insert/update process altogether?

Any ideas why you can’t return data from any of the Channel Entries API Extension Hooks?