Is it possible to select parts in an assembly and convert them to a sub-assembly without affecting the original assembly.  What i mean is that if i have an  assembly with parts a,b,c,d,d,f,g in it and i want to make parts a,c,f into a sub-assembly, but yet keep them in the original main assembly.  Either make an external assembly file or a new sub-assembly in the main assembly. SO the main assembly would now have parts a,b,c,d,e,f,g and sub assembly hh which contains parts a,c,f. 

Thanks