I created a new installation, and I want to send membership reminder to everybody who is, say, 2 months or less before expiration (including those whose membership already expired). Essentially, the opposite problem from the one described here. Is it possible?
This answer assumes that this is a one-off requirement to deal with the "backlog" of reminders that has arisen because you haven't had the ability to send scheduled reminders before and that once the site is established you will be sending reminders at 2 months before the membership end date.
You wouldn't do this with a scheduled reminder. You would use Advanced Search or Find Membership to identify all those who "missed" the two-month-before reminder and send an email to them using CiviMail.