Once saved as an Iges or parasolid the file is a dumb solid you will have no tree just an imported part(s) with no history.
Sorry, you can't do that. You will end up in SW07 with a dumb solid. Use Parasolid, not IGES, as it is much more likely to give you a good model. If the part is reasonably simple, you might be able to use FeatureWorks (provided you have it) in SW07 to build a new feature tree.
Actually, I just reread your note. You say an assembly, and then talk about the feature tree. Do you need to modify the parts in your assembly or just modify the assembly? The assembly will also be a dumb assembly, with no mates, but everything should be located in the same place it was is SW09. You should be able to get by with only floating and then mating the parts that need to move.
Thanks for your response Jerry.
Thank you for your response.
The file is a top down assembly file where I have built all the parts off the layout sketches.
Shame as I will be able to use some of the parts but the file still is currently working and maybe will need some remodelling,