Your entire post makes no sense whatsoever. What do you mean you want to download the PMDG 737 in the default 737-800. They're both completely different airplanes. The 737-700 is also a completely different airplane, so I'm not sure what it is you're trying to accomplish.
What I am meaning if this makes sense. I have a CFG file for the 737-800. Can i copy and paste the download for the 737-800 PMG onto this CFG file with other 737-800 aircraft or does this have too have it;s own file for the PMG 737-800 or 737-700