How do I change the name of the same part in each assembly configuration?

I built three different configurations in one assembly. 

I wish I could change the names of the same parts in the different configurations and be able to save them externally in DXF and SLDPRT.

You have to go through custom properties configured at the part and configuration level in the ASM.
So it won't be the name but the designation.

In my opinion, this is the cleanest solution even if for me if 2 rooms have the same topology then there should be only one.

OK. So we can't really change the name of the piece.

However this piece has two different lengths and I have to take out two different DXFs for the cut.