Try this....
1) Put the following entry into the NPCShips.ini
[NPCShipArch]
nickname = fc_lr_pi_ss_elite_d7
loadout = fc_lr_pi_ss_elite_loadout01
level = d7
ship_archetype = pi_ss_elite
pilot = pilot_pirate_med
state_graph = FIGHTER
npc_class = unlawful, class_fighter, d6, d7
2) Now open the factionprops.ini and comment the following line out (simply put a ; in front of the line)
npc_ship = fc_lr_pi_fighter_d6
npc_ship = fc_lr_pi_elite_d7
should now look like....
;npc_ship = fc_lr_pi_fighter_d6
;npc_ship = fc_lr_pi_elite_d7
3) Add this to your factionprops.ini
npc_ship = fc_lr_pi_ss_elite_d7
4) For the encounters... the actual spawning of 3 ships, you REALLY don't need that. The encounter called "area_assault" works just fine. Just ensure you have some spawn zones in the the systems you want with difficulty 7 specified.
Example:
[zone]
nickname = Zone_BloodGuardianSpawn_001
pos = 0, 0, 0
shape = SPHERE
size = 200000
sort = 1
toughness = 7
density = 3
repop_time = 20
max_battle_size = 4
pop_type = background
relief_time = 20
encounter = area_assault, 7, 0.800000
faction = fc_lr_grp, 1.000000
encounter = area_defend, 6, 0.200000
faction = gd_bh_grp, 1.000000
Im tired as hell... so I might have forgot soemthing or made a simple error. But it should work. Good luck