It is easily possible.
The easiest way to do this is to extract your ep4.5 client as well as an ep5 client.
Now take the ep5 files you want(3DC, MLT, etc files for armors/weapons) and add them to your ep4 client.
Now you can either throw in an ep5 item.sdata into your ep4 client or manually add ep5 items to your ep4 sdata.
All this can be done with mobs, npcs, or skills as well.
Don't forget to configure your database as well for this.
Easy stuff just takes time

(Due to the fact I know someone will post this...You can use Castors tool to do all this...)