LAN Invalid MAC address workaround (Nighthawk router)

Found this issue that applies to my Nighthawk router: https://community.netgear.com/t5/Nighthawk-Wi-Fi-5-AC-Routers/LAN-Invalid-MAC-address/m-p/22662041

In my case, I have a Nighthawk X6S, model number R7900P. Firmware version is V1.4.4.94_1.3.56.

It's been over a year since that issue was closed, and the solution they landed on is "downgrade to old firmware, then upgrade again when you're done changing IP reservations". I'm not satisfied with that solution for such a trivial bug.

So if you're handy with your browser's debug tools, there's a really easy workaround I'd like to document. Maybe it will help somebody. Here's how you do it:

1. Do everything you'd normally do to assign or change an IP reservation, up to the point of clicking the "Apply" button.

2. In the dev tools, search for "function checkData" (press Ctrl-Shift-S to open the global search).

3. Once you've found that function, put a breakpoint on the last line of it ("return true;").
4. Click the "Apply" button.

5. Execution should pause at the breakpoint. Now, execute this in the console, replacing <your mac> with your mac address, all caps and including colons: cf.rsv_mac.value = '<your mac>'
6. Now resume execution in the dev tools. The request should succeed.