I found the perfect solution for you it is a little program called iPhoto Library Manager:
They have a free and a pay version.
You can do these things with it:
-Split a large library apart into smaller, more manageable libraries
-Merge multiple libraries together into one
-Create multiple iPhoto libraries, instead of having to keep all your photos in a single library
-Copy photos from one library to another while retaining titles, comments, keywords, ratings, and dates
-Switch to another library with one click by using shortcut files
This sounds like the perfect solution for you!
If this answers your question, please kindly select * ACCEPT * so I can be rewarded for my efforts.