Replacing cvt filter and fluid

My daughter has a 2008 Nissan altima and we are going to
be replacing the cvt stepper motor this weekend.  I have
the part ordered already but just a question about the rest.  
We are going to replace the filter and gasket since it will
be accessible.  How many quarts of cvt fluid will need to
be replaced after dropping the pan?  Will it drop all
11.quarts of fluid when I take off the pan or will I only have
to replace a portion of it.  I need to know so I can get
enough cvt fluid and also, should I use oem Nissan fluid or
can I use something else.  She is 19 and just bought this
car used about 3 months ago so I don't want it shooting
craps before she has a chance to pay it off.