Relating Existing Projects to Countries(in Team Complete Project Manager sample app)

Hello,

Reference here is the "Team Complete Project Manager sample app", Table to consider is:

• Project
  
  

Let us just say after addition of 50 Projects there comes a need of relating them to countries which basically means "A Project is running in one or more countries".  Countries were not in the picture when the app building initially started but is required now.

For this the Countries table was created(storing just a list of countries) & related to the Projects table(type Text (reference proxy) on Project Name), what would be the provisions of relating existing 50 Projects to their corresponding Country values?( I was exploring usage of API_ImportFromCSV, was wondering if there are more efficient ways to do this in case existing Projects number is much larger than 50?) 

Also 1 Project can have many countries so it has to appear as multi select field in the Add Projects form.

Similar need is encountered in a real application, Please suggest.