As I said, yes. If you won't do it, you leave traces of the old/alt account, which is not ideal and defeats the purpose of having an alt account.
For example, if you going to have an alt account for the duration of the subscription, then always use that alt account until it ran out.
Then, when you want to go back to your main, do what I've suggested above.

This way there is no risk at all to lose your main account.