The backup files for the routers I have all have the least significant byte
first for the 2-byte integers in the data. That's most likely because all of
them use similar CPUs, and the data's actually in the native byte order of the
CPU. These programs may need modified so you can tell them the byte
ordering. I've marked the places in the code where that needs to happen with
TODO markers.
There's several static buffers in the program that're based on the assumption that single values don't exceed 64K and NVRAM images 128K. That's probably true for current routers, and it makes the code a lot simpler to just allocate fixed-length buffers in the source code. I should probably go back and pull those assumptions into a header file and fix the code to use symbols and macros.
The DD-WRT team will most likely consider these programs unofficial and unsupported. If you use them to build backup files and load those files into a router, you're on your own. The same is true for me, the DD-WRT team may change the backup format or the process of loading the backup into NVRAM without warning causing files produced by nvram_build to suddenly start doing anything from failing to load on up to bricking the router. Use caution when using these tools to edit backups and reload them into the router.