Brother Hesychios is correct in principle. A dispensation does not actually relax a rule or regulation, because the rule or regulation is still generally in effect. What a dispensation actually does in essence is remove the normal canonical penalty for not obeying a law established by the Church.
If you search online, you will find sources from EO bishops who say contraception is a sin and permitted under oikonomia. I’m sorry I don’t have links for you, but I know I’ve seen and read them in the past. You can do your own search online if you are willing.
True, but the Church has given dispensations for soldiers in time of war. Again, it is not a license to kill (shades of 007!). It is simply a removal of the Traditional penalty associated with killing.
Blessings,
Marduk