Large .stp File From NX10 to .SLDPRT

I have joined a new company which uses Unigraphics NX10. The project I'm working on was designed using NX10 and i need to convert the .stp files so that I was able to change part sizes and add new parts.

i have tried importing the the .stp file using "import assembly as multiple body parts",

My problem with this is that if i chose to edit feature it gives me the prompt :" Replacing part file by assembly file is not allowed". Also the names of parts is removed and are simply called "Product Structure.stp [1]". Considering that i have close to 200 parts i need the original names.

Any advice and/or help will be hugely appreciated

PS. I am unable to use NX10 as no more keys are available

SolidworksImport/export