No, you can't. If you flash the Rogers pre-portico, and then update OTA, which is necessary in order to be able to flash the AT&T dev ROM with Amber, you are then stuck. From that point on, you can no longer flash the Rogers pre-portico update again, which means you can't go back to the AT&T ROM ever again.
The 'AT&T Dev ROM' isn't really an AT&T ROM at all, either. it's just an unbranded version of the Rogers ROM. As I've already said, I don't recommend flashing it either. I've had major issues with it. Internet Sharing worked for a week after doing the Mexican keyboard thing, but it's completely broken now (I pay for it)... and live tiles don't update either. So like I've said much earlier in this thread, I really don't think it's a good idea for most people to be doing this procedure.