You can import the tags from the file into the MC database. Select a file, right click, select Library Tools and Update Library (from Tags). That copies the file tags to the library. The tag names need to be the same as MC uses - e.g. Artist. Try a few and see if it does what you want.
There is a SWAP function which will swap the first and last name, but it is by no means perfect. For example, it does not always do the right thing if there are 3 names in the artist name. You can use it going forward, but to start you should be able to update the database with your existing tags.