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First of all let's clear the misunderstandings - the EPROM is not the memory to store any "program" or "project". Downloading the EPROM changes ONLY the firmware of the controller. The program in AC700F is battery backed - this means that as long as You have a functional battery in Your PM 783F module, Your program is safe.
Now if You don't have batteries for all Your AC 700F and You will lose the program (by initializing the controller or by lost of power supply) You must either load the program from CBF or, if you use the most reacent version of firmware, You can restore it from backup on a SD card. No EPROM download is required.
Now to Your questions:
1. When you download the EPROM it initializes the controller so there's no program loaded to it.
2. The procedure after loosing the program is to simply do a download from CBF. If you would like to do a backup on a SD card follow procedure described in here:
3. EPROM is only for your Firmware, the program is stored in battery-back RAM.
Hope it cleared things a bit.