You may or may not have came across this, but sometimes when you are trying to override an asset it doesn’t work. While this does work with a mod but not with a map.
To enable overriding you have to search for the asset you want to override. This can be found here:

Black Ops 3 Root\zone_source

I recommend using a Text Editor that supports folder search. This makes it a lot easier to find the line you want to comment out.

Example

You want to override lets say the Jugg perk icon, in the zone file of your map you add this.

image,specialty_giant_juggernaut_zombies

Now you search for the same line in the files that are located in the “zone_source” folder. In this case it can be found in:

Black Ops 3 Root\zone_source\all\assetlist\zm_levelcommon.csv

Comment out the line like this:

//image,specialty_giant_juggernaut_zombies

And that’s all.