Requirements:
We need two tools for making this mod.

First one, Archive2 help unwrapping and wrapping files.
It comes with the Fallout 4 creation kit downloaddable for free in the launcher, no need of Fallout 4.
Once installed, by default you can open Ba2 files (.ba2) by just clicking them.

Secound one is Jpexs for editing swf (Flash Player) files.
Jpexs: https://github.com/jindrapetrik/jpexs-decompiler
Check release section for download and get the latest one.

The making:
Navigate to Bethesda.net Launcher\games\Fallout76\Data
Open SeventySix - Interface.ba2
Extract only one file not all of them: interface/mapmarkerlibrary.swf
Open interface/mapmarkerlibrary.swf with Jpexs.

(solved with latest jpexs version) If you get interface glitch, close it and open via the shortcut or directly the exe. It will open last file open.
That for me solve performence and interface glitch with windows 10 making it unusable otherwise.

For svg edit, look inside the shapes folder. You can visualize them by clicking on it to make sure it's the right one.
From there you can extrat the original svg and edit them with gimp, inkscape or just notepad++ like I do if you know more svg code.
Take notes that I verify the file header of the svg to be the same idk if those programs modify it or use some uncompatible transformation code.
For replacing the svg, go in Jpexs inside shapes folder and simply righ click the image you're editing then hit replace.
When done with the swf, add it inside an empty Ba2 file but, respecting the folder tree it was found in. Here it's interface/mapmarkerlibrary.swf
Then finally if you haven't done it yet, edit INI file to load that mod you named above, the Ba2 containing the only swf we edited.