All, to be clear, I realized the OP never actually stated this - it's only been implied:
- the firewall needs to be off because the WAN port will be used to re setup the OpenWrt (or initially install it)
- whatever state the device is in, the OP has reset it (or it's in a new state - i.e. WiFi off by default)
What I'm confused at is the need for a IntramFS image. It seem the OP's intention is to do initial installations of OpenWrt on equipment mounted in unaccessible locations.