The Martyrs of Libya, and Prayers for the Dead

I prayed the Rosary the morning at church, with a group with whom my Mother used to pray, (I feel especially close to her sometimes at weekday Mass, "inherited" her seat, you know - and her place in line to lead a decade from time to time.)
I had been thinking about indulgences and prayers for the dead and how I would explain them and the treasury of merit, (and how that works into the economy of salvation, kind of the way you dad let's you think you're helping him when you're four years old and want to shoulder some of the load when he's doing yardwork,)  to the kids in CCD, (as they call it here.)
I flashed back to my parents talking, when I was very little, about someone very, very dear to us, and quite unknown to the larger world, who had just died, at the same time as someone very famous; and my Mother talking about how sad it was that so many people would pray for, and say Masses for this famous person, and very few would give a thought to, or even knew of "poor J." (In retrospect, the famous dead Catholic was probably in FAR greater need of prayer and reparation than dear, sweet "poor J., but that's not the point.)
How often when someone dies we Catholics are uncertain of his fate --- okay, ya pretty much know if someone's a complete scoundrel, but your average trying-but-occasionally-stumbling Joe --- who's to know if he died in a state of grace, or instead needs a little bit of washing and buffing in purgatory, or what?
You don't want to fail to offer prayers for someone you love, but you don't want to insult them either, right? (Imagine someone, for instance, some early Christian who knew that the Blessed Mother was a very sweet old lady, but not , of course, that she had been immaculately conceived ; now imagine that someone praying for her soul after she had left this life!)
Well, of course, nothing goes to waste in the economy of salvation, so that's not really the issue, but how about this?
Can I put my prayers, any indulgences such as I may gain, any merit I might accrue from, (for once uncomplainingly?) suffering -- can I put them at the disposal, so to speak, of the beloved departed? tell him or her that if he or she has no need, to just... spread them around where they'll do the most good?
So I have decided to make someone I knew and loved the executor, the Trustee of my assets.
Is that acceptable? (I know when I get schemes they are often hare-brained, and often, if not heretical heresy-adjacent.)
Do those 21 Coptic Christians who died confessing the Lord Jesus need my prayers? Very likely not.
But I can pray for them nonetheless, and if they're just coals to Newcastle, the Trustee will apportion my... heavenly holdings.
Orate pro nobis,

Milad Makeen Zaky
Abanub Ayad Atiya
 Maged Solaiman Shehata
Yusuf Shukry Yunan
Kirollos Shokry Fawzy
Bishoy Astafanus Kamel
Somaily Astafanus Kamel 
Malak Ibrahim Sinweet
Tawadros Yusuf Tawadros
Girgis Milad Sinweet
Mina Fayez Aziz
Hany Abdelmesih Salib
Bishoy Adel Khalaf
Samuel Alham Wilson
Ezat Bishri Naseef
Loqa Nagaty
Gaber Munir Adly
Esam Badir Samir
Malak Farag Abram
Sameh Salah Faruq
Another worker from Awr village whose name is not yet known.