No, you cannot pause Migration Assistant. You must either let it finish or stop it completely and start all over again.
If you're doing it via Wifi you could try just leaving the area and seeing if it restarts when connected to another network but I wouldn't recommend it. Who knows what would happen in that time of disconnect.
Don't stop it. Let it finish. Then you can erase the account that it created (unless you did this the first time you booted your Mac, in which case you wouldn't want to stop).
The best time to migrate is the first time you boot your Mac in Setup Assistant. If you messed up I would re-install OS X by booting up holding command-r keys into your Recovery Volume.
The screen should give you these choices...
Restore from TM backup
Reinstall Mac OS X
Get help online
Choose re-install and then be sure to migrate in Setup Assistant when prompted.