When modifying Project Wingman assets such as occlusion/roughness/metallic (ORM) maps, normal maps, or models, the files in question will need to be exported from the game's main pack before they can be edited in any useful way. Moreover, it's simply useful to have a handle on how Project Wingman organises its files. This is where UEViewer, more often referred to as UModel, comes into play.
A link to UModel, alongside other useful tools, can be found on the Useful Tools page.
After downloading and extracting UModel, navigate to the game files in the UE Viewer Startup Options. For Steam users, this would most likely be C:\Program Files (x86)\Steam\steamapps\common\Project Wingman\ProjectWingman\Content\Paks. Check Override game detection, and select Unreal engine 4.24 in the dropdown menu. Finally, check the export-only types if you want to export audio files, then click OK to open the Project Wingman assets.
At this point, you can export or simply extract individual files or entire folders. Opening the Objects folder and right-clicking Aircraft, for example, will allow you to export the folder content, choosing a particular directory for the assets to be exported to as well as file formats for exported objects. ActorX (psk) and ActorX (pskx) are the most useful options for exporting skeletal meshes (i.e., models), and TGA is generally fine for exporting textures. All other settings can generally be left to their defaults.
Exporting generally converts files to a more immediately useful format, where applicable. This is particularly the case for textures, audio files, and models, but UModel can't export everything: data tables, audio cues, and similar files must be extracted, instead, preserving their cooked Unreal Engine file format.
Whether modifying meshes, textures, audio, or data tables, your modified files will eventually need to be packed so the game can load them. Currently, u4pak is the most common method for handling this in Project Wingman modding.
Again, a link to u4pak can be found on the Useful Tools page. As noted therein, u4pak also requires Python to be installed.
u4pak can be used in several different ways, as documented on the tool's GitHub page. The simplest ways to use the tool for Project Wingman mod packing are either via Python's Edit with IDLE function, or with a simple Batch script file.
Packing mod files requires a recreation of the game's file structure – a structure visible in UModel as well as when assets have been extracted. You should create a ProjectWingman folder in the same directory as u4pak, and within ProjectWingman create a Content folder. From here, simply recreate the file path for any assets you're replacing. An F/C-16 skin replacing slot 01, for example, would consist of the file path ProjectWingman\Content\Assets\Objects\Aircraft\F16C\Textures\Skin, with the Skin folder containing your texture (F16_01).
The PSM Custom Skins Guide contains instructions on the necessary file path for Project Sicario Merger-compatible skins, as another example.
Two methods can be fairly easily used to create new .pak files when working with mods:
Right click u4pak, and select Edit with IDLE. A Python window will open. Press Shift+F5 to open the Run... Customized interface, and type pack MyTestMod_P.pak ProjectWingman and click OK to pack a mod from your properly-configured ProjectWingman folder. The resulting .pak file can be renamed however you like, so long as it ends in _P. If the .pak file does not end with _P, the game will not load it properly.
To make packing quicker, you can also simply open Notepad, Notepad++, or your other text editing software of choice, and create a simple Batch script. Paste the following into your text editor of choice:
@echo off
"C:\path\to\Python\Python39\python.exe" "C:\path\to\u4pak.py" pack MyTestMod_P.pak ProjectWingman
set /p temp="Press enter to continue"
Fill in the correct paths to python.exe and u4pak.py, then save it as a .bat file in the same folder as u4pak. Running the Batch script will have the same effect as following the Edit with IDLE instructions, but is much quicker.
Python's exe file may be located in your AppData depending on how you installed it, e.g.,
C:\Users\username\AppData\Local\Programs\Python\Python39\python.exe
Right click u4pak, and select Edit with IDLE. A Python window will open. Press Shift+F5 to open the Run... Customized interface, and type unpack pakName.pak and click OK to unpack the .pak file named pakName.pak into its own folder.