Please make your changes to base prototypes in data or at least data-updates so I can copy them with correct properties while still giving other mods a chance to see prototypes in final-fixes without enforced load order.

Generally anything that is done in final fixes is only done in final fixes because it's undoing something that another mod did in data updates (or in some cases even in the final fixes stage, introducing load order dependencies). The override file is 2.5x larger than the override_final. Nothing was done in the final stage gratuitously.

Again, please make changes to base prototypes in data or data-updates.

With only Nullius loaded:

   1.693 Script @__test__/data-updates.lua:9: {
  flags = {},
  icon = "__base__/graphics/icons/small-electric-pole.png",
  icon_mipmaps = 4,
  icon_size = 64,
  localised_name = {
    "entity-name.nullius-power-pole-1"
  },
  name = "small-electric-pole",
  order = "a[energy]-a[small-electric-pole]",
  place_result = "small-electric-pole",
  stack_size = 50,
  subgroup = "energy-pipe-distribution",
  type = "item"
}

   2.179 Script @__test__/data-final-fixes.lua:3: {
  flags = {},
  icon = "__base__/graphics/icons/small-electric-pole.png",
  icon_mipmaps = 4,
  icon_size = 64,
  icons = {
    {
      icon = "__nullius__/graphics/icons/entity/pole1.png",
      icon_mipmaps = 4,
      icon_size = 64
    }
  },
  localised_name = {
    "entity-name.nullius-power-pole-1"
  },
  name = "small-electric-pole",
  order = "nullius-bb",
  place_result = "small-electric-pole",
  stack_size = 100,
  subgroup = "electric-pole",
  type = "item"
}

One significant exception is that box icons are finalized in the final-fixes stage. This is because so many things are updated by other mods in data-updates or later that some of the box icons will look different from the actual icon if they're done earlier. However, most of the boxes don't change, so most of the boxes could be done earlier, but they can't all be done earlier and it's easier to do them all in one pass. Perhaps it could be done redundantly in both passes, so that the boxes are mostly correct, and then fixed later. That would be slower but possibly more friendly to other mods. But if it's not 100% done that may not be good enough anyway.

Note that on the FAQ tab of this page, there is an entry on modding for Nullius. The most common issue that people run into with Nullius mod compatibility is with it disabling recipes. You're not meant to have to do stuff in data-final-fixes to keep Nullius from doing that, and there are many existing examples of porting mods for Nullius.

If I knew what you were working on I could give more targeted advice. But definitely nothing was really added to final-fixes carelessly. It was always done in data-update first and then moved to final-fixes as a last resort when that didn't work.

Again, please make changes to base prototypes in data or data-updates.

That's because other mods try to change those things, so the changes wouldn't stick if done in data-updates. Nothing was added to final-fixes just for fun.

This is not a about box icons, but the properties of item and entity for base power poles.
Only your final fixes changes
item icons, order, subgroup, stack_size
entity icons, maximum_wire_distance, supply_area_distance, fast_replaceable_group, next_upgrade

Lighted Electric Poles + copies all pole prototypes to created lighted variants in data-updates. At that point Nullius still uses base property values.
If you just also did your property changes to base entities in data LEP+ would perfectly work alongside Nullius without issues.

OK. I will make all power pole changes in both updates and final fixes.

Thanks.
Please also make sure recipes and technologies are the way you want them to be in data-update so I can find and add my recipes alongside them.