Set up the pose as you wish. When you are satisfied with everything click on the Pose tab, then Custom and finally click on the + at the bottom right to save it. Next click on the Project tab, Custom, clothed and with the + add your project to your custom content. Finally, right click on your newly saved custom project and select "Set as Default Project" from the list.
Next time you launch Character Creator 3 your saved project will be automatically opened, if you add a new Avatar to the project you just need to click on "Load Avatar" and the new one will be loaded with your custom pose.
System: Win 10 Pro (1803), Asus X99-E WS, CPU i7-5930K -3,5 GHz, 32 GB DDR4 2666-16 RAM, NVidia GTX 1080 Ti GPU - 11 GB VRAM(Driver 417.35), Samsung 850 Pro 512 GB SSD, 6 TB HD storage.