Hi Adam,
Namemapping functionality is one of the things that you must consider really good and make a well-grounded decision on whether to use it or not and how to build the architecture of your tests in case you decide to use namemapping.
The case here is that namemapping cannot be shared between projects. The only thing you can do is to merge (import) namemapping from another project into your current one and manually resolve the conflicts. If the mapping of some object changes you'll have either to correct namemapping scheme in all relevant projects or to correct it in one place and merge it one more time into all other projects and resolve the conflicts one more time.
My advise would be to spend some time for playing around with namemapping to see how it works for you and does it fit your requirements (localization, unstable objects' hierarchy, etc.).