Mark, it is not impossible to break up. You can start by importing the gedcom into a desktop genealogy program, then export a gedcom from that which only includes - for example - your maternal great-grandmother's family. If that's still too large, then go back one more generation to make the splits. You will end up with several gedcom files, all small enough that they can be imported to WikiTree one at a time.
As to your previous WikiTree account, you can write to info @ wikitree.com (without spaces) and ask if they can combine your current account with your old one. The good news is that you will have that many fewer people to import from your gedcom, since probably many will match the ones you already added here.
