It is possible. MARCOS worked along side Navy SEALs during that period.
But it is also true that Para SF and Green Berets regularly exchange badges in joint exercises like Vajra Prahar.
I'm sorry but no, SEAL Trident's are a unit designation, they are not swapped, traded etc. You only get one if you go through BUD/S.
Badges/jump wings etc are different they are skills designations and if you jump with another unit you can get and wear their wings.
Challenge coins/unit mascots etc are just traded because guys in OPT's trade shit..