Is it possible to reuse shingles/replace only part of the shingles?
I would say yes for sure on this.  You are going to have to pry them off more carefully.  Note that the nails/staples should only be under the other shingles.  If put on wrong it could make it difficult to reuse.

The only reason I am suggesting reusing is that you met two criteria:
1. You have a small area and you don't want a color mismatch.
2. That area is outside of a living space.  

I would personally reuse them.  I would try to keep the row(s) between the house and porch attached if you can.  This will be your we spot and you will need to retrofit that first row under.  You would want this on the porch in case of future potential leaks.