Is there a way I can sign in to iTunes as another user?

Yes. Sign out of the iTunes Store, then sign in with a different Apple ID. Sign in to the iTunes Store, Mac App Store, and iBooks Store on your Mac - Apple Support

In general having more than one account, particularly for apps, makes things overly complicated.

tt2

Please also see the info on 'associated devices'…

View and remove associated devices in iTunes - Apple Support

You may end up locked to an account for 90 days depending on what features you enable in an Apple ID.

Good point. 🙂

tt2

You're welcome. 🙂

tt2