Has anyone tried booking through their travel agent, using their normal corporate discount code, but using the promotional code here?

Curious about whether that would work...

Concern is that I think my firm requires us to use the corporate discount for low (perhaps because I would not have insurance coverage if I don't use the corporate code).

Alternatively, if creating the original booking through United.com is required, I wonder if then going to Hertz.com and changing the corporate discount to my firm's but leaving the promotional code in there would work?