Alternate characters will indeed be allowed on Shinobi Gaiden. However, there will be certain stipulations on alternate characters.
For starters, you need another account for your alt character. No biggie, just make another account and its all good. Won't get in trouble for spamming
Two. you CANNOT EVER interact with your alts. This is absolutely forbidden in all ways shapes and forms.
Three, you can have up to three alts. Simple as that.
Four, you cannot have more than one ninja residing in the same village at a time. Sorry
Five, if you are seen as inactive with any of your characters, they can, and just might be archived.
Six, you may only start with one character above D rank.
Seven, your alt character can not be in the same clan as your main. Don't be selfish let someone else have a spot.
Note: Three villages are closed right now. If you want a ninja in Iwa, Kiri or Suna that starts at above Genin, you will need to wait to make your higher ranked ninja for those villages. Otherwise, you will be forced to get rid of your first ninja that was made over D rank.