You can yes.
Functionally it would be the same. RAM kits are tested to make sure that all the sticks work on the same level as each other to prevent instability and to get the best possible performance. Mixing kits even of the same model isn't guaranteed to work perfectly, while a larger initial kit is.
However in my experience, I haven't had issue doing it. In all likelihood you'l be fine.
Thank you very much for the quick response!
Though thriftily, it may be more intelligent to buy the initial larger kit for the time being! (;
You have dispelled this doubt that I have had with this memory.Thanks again