You could customize player image for your specific needs wither for configuration or branding in number of ways.
1. Bootup video and welcome screen - You can upload your own assets to your account (using the same method Add files under Assets tab) and deploying to the groups. More details are available at https://help.pisignage.com/hc/en-us/articles/360001372931-Special-assets
2. Server and wifi configuration - You can download the SD card image and mount it on a laptop. The /boot partition is visible under your laptop OS. You can create a file name player-config.txt under /boot partition and add the following lines
3. Customizsed SD card image with your additional software for white label servers - Request for the base image at firstname.lastname@example.org. With this image boot the Pi, add additional assets and software modules, run the supplied script and prepare your own image