as he called it a mod, my guess would be its based upon tweaking the limits in the software application, which would likely have issues with your warranty,
Otherwise it may be just like my SAG1021 (AWG mod for scope), where there SCPI commands are not restricted like the UI options are, e.g. +-4.0V signal offset instead of +-1.5V via the UI,
Just checking on my option AWG, i can easily set periods up to 1,000,000 seconds long for my waveforms via SCPI