Manual or normal weapons profiles last as long as the profile is selected or the duration of the mission computer session in the cockpit respectively. There's no known way to have persistent (session to session) or otherwise altered default (DCS generator) profiles.

When the "M/" profile is deselected, it's gone. Several people have had problems with getting auto-lase LGB profiles to work and it was later discovered this "bad habit" method was the culprit. They were setting up their profiles correctly but deselecting them and ended up inadvertently reverting to the defaults during actual delivery.