Can any person in any church or institution outside of the temple in fact be sealed by the Holy Spirit of promise?
Yes. Some people have received a witness that they had been sealed to their fiancé before they were even married. They felt certain of this sealing and they only went through the temple sealing for the benefit of others who they knew would not recognize their spiritual ordinance, including the church. But they knew without question that God had recognized their covenant and commitment to each other, and ratified it by the spirit.
Let’s face it, most ordinances are based on decisions made in advance or after the fact. For example, baptism is the commitment to follow Christ. Very rarely does a person actually decide to make that commitment and covenant at the time of baptism. If they are being baptized for the right reasons, then the commitment and covenant is being made before baptism. And if they are being baptized for the wrong reasons, it is being made after baptism.
The spirit will not ratify the covenant or commitment until it is done for the right reasons. And when the decision is made, and the covenant is made, it is ratified whether that determination to follow Christ comes before or after baptism. It is the same with every ordinance and covenant.