How to Change Map Marker Size on Pip-Boy World Map.

Step 1: Extracting the Interface Files.
Using BAE (Bethesda Archive Extractor).
Select File > Open File...

Navigate to your Fallout 4 Data folder.

To find this location on a Steam installation:
Right-Click Fallout 4 in Steam and select Properties.

Click the Local Files tab.
Click the Browse Local Files... button.

Select the file: [Fallout4]\Data\Fallout 4 - Interface.ba2
Extract the data files:
Interface > Pipboy_MapPage.swf
Interface > fonts_en.swf
(Note, lowercase sorts after uppercase, fonts_en is near the end of the list)
Done.

Step 2: Opening the Map Interface for Editing.
Using JPEXS Free Flash Decompiler.
Drag and Drop, or Open the newly extracted Pipboy_MapPage.swf
The file requires an import of the fonts_en.swf, select Yes from the Warning Popup.
Done.

Step 3: Setting Up Map Marker Sizes for Editing.
Select scripts > MapHolder
We need to add an overwrite variable to the Marker Scale traits.
Scroll Down the ActionScript to about line 160.
This line starts with "addEventListener".
We are going to add new lines before this line.
Place the mouse cursor on that line.

The right-hand side should light up with code, this is the code we need to alter.
On the right-most frame (Method/Getter/Setter Trait), click the Edit button.
(Never use the middle frame to edit!)

Insert the lines:
getlocal_0
pushdouble 2.0
initproperty Qname(ProtectedNamespace("MapHolder"), "MARKER_SCALE_MIN")
getlocal_0
pushdouble 0.5
initproperty Qname(ProtectedNamespace("MapHolder"), "MARKER_SCALE_MAX")
Note: Do not create any blank lines.
Click the Save button on the Right-Most frame.
Click the Save button in the File tab in the Upper-Left of the JPEXS Window.
These are the default values.
Done.

Step 4: Edit the Values.
MARKER_SCALE_MIN does most of the magic.  Higher values make Bigger Markers.
As an example, to cut the Map Marker Size in Half, change the value to 1.0.
Go back into Edit in the Right-Most frame.
Change the pushdouble 2.0 to pushdouble 1.0
Save the Edits, Save the File.
Check it out in game.
Done.
Extra Tip: The game reloads this file every time the Pip-Boy is brought up in game.  This means you can save the changes, then toggle the Pip-Boy off and back on in game without have to quit the game and restart.