No. Your projectfile, the .mpr-file, contains all information on your project (except for the widgets).
Yes, you can move those file from one directory to the other, but upon opening the moved .mpr-file, you will see its content is as it was in its previous location. If you opened it by using Mendix Studio, it will recognise the difference in version.
Not sure what the purpose of your requirement is, but if you need to move to the higher-versioned project-versionb, but still need some of the documents that you have in the lower-versioned project-versiona, the way to go is export those document from projecta and import them in projectb.