Based on the information written on the above site, I tried to download Barrier Breaker and Attitude Adjustment version of ar71xx-generic-wzr-hp-g300nh2-squashfs-factory.bin from genuine firmware , None of them failed.
However, the DD - WRT file downloaded from the link on the site 's Installation procedure has been successfully written.
Can I install only DD - WRT on this wifi router and can not install OpenWrt?
If you can, which file should be downloaded and installed?
The only known-safe procedure is to first revert to the Buffalo OEM firmware (DD-Wrt should have some information about how to do that) - and then to install OpenWrt from there.
If there would be a shortcut avoiding this intermediate step is device specific (does DD-Wrt change anything in regards to the bootloader and/ or partitioning, relative to the OEM firmware), just trying this without knowing for sure about these details entails a huge risk of permanently bricking the device (and we don't know how/ if DD-Wrt has done any of these potentially dangerous changes for the wzr-300hp). The only safe advice here is to go the long(er) way, which is known to work.
Leave the LED for last, if you've gotten everything else working to your satisfaction, you can take a look at System/ LED Configuration - if everything else fails, electrical tape has been a proven method.