Yes, you can name them however you want, but they will run in alphabetical order (which is why laravel timestamps them). Also you can change a migrations name after the fact (you've already run the migration). You just need to change the filename in the migrations database table (so it can find it to roll it back) in addition to changing the actual filename and classname.
I'd use a 3 digit number for the prefix. (001_migrationname) to leave enough room for future migrations. You never know.