Is it possible to use the pins “USB D-” 36 and “USB D+” 37 to add a USB connection that works for programing?
Chapter 46 (starting at page 235) of this document outlines which peripherals can be used to access the system bootloader.
Unfortunately the USB HS1 peripheral (pins 36/37) are not available. However, there are a few other peripherals that can be accessed from the pinout, though I have not personally tried to flash the daisy through these pins (yet).
The ones that are broken out to daisy include USART2 (PA2/PA3) , I2C1 (PB6/PB9) and SPI1 (PA4, PA5, PA6, PA7).
There are USB->Serial cables that work for programming via serial on other boards. So you might be able to have a USB port that connects to the USART2 pins, though it would not be capable of actual USB communication.
Thank you for the info and sharing that document. I have not seen this document before. Very helpful.