See https://forums.dfworkshop.net/viewtopic.php?p=27184#p27184 for Kaedius' helpful post I have reproduced here. This info enabled me to add the Archeologists Guild ...

Change the .fbx file association to blender_to_os.bat. To do this, right-click any .fbx file, click Properties, and change the Opens with preference. Click on more apps↓, scroll down and select Look ...