If I'm reading Gyathaar's post right, you just need to pick up a save, open it in 1.61, enter the admin password, (play+save it?), then open it in 1.74 and lock it again.
This is my one question - do I actually have to play a turn?
Can I just open the current save in 1.61, unlock it, save it without moving, open it in 1.74, lock it, and then save it again without changing anything?
Basically, do I have to make non-reversible moves? Perhaps I will try later tonight just to see if it works...