Pretty sure you could by editing the supply crate spawning voumes but then that would require you add the newly edited full map to your mod I do believe.
There are 4 loot item sets, 25 through 60. Level 25 loot item set is called from a level 25 drop, level 25 and 35 loot item sets are called from a level 35 drop. 25, 35 & 45 loot item sets are called from level 45 drops and so on. That’s probably why you did not notice a change. In my supply drops mods, I removed all the calls to the lower level items (you only get level 45 loot item set from a level 45 and so on) and it has worked out pretty well & consistently.