I'd make some substantial changes with actual creativity, not artistic license. The Covenant characters are pretty grounded by this point. Yes, Bungie brought in Skirmishers and they've tweaked the Elite design in a few different ways over the years. Yes, Bungie changed the Brutes fairly substantially from H2 also to make them more dynamic. Not all of those decisions were great. The point is, the Covenant have a look and feel that the change to the Jackals and that ridiculous Brute concept just don't fit.

343 had/has the opportunity to create from scratch. Instead they made largely uninspired Promethean baddies that look almost like plastic play toys (maybe that was the point, marketing and all and action figure lines) than anything awesome or scary. H5 CGI thing? Oh no, it's another really weak looking glossy plastic figure! It's just really big! Chief sure doesn't look concerned. Sure, maybe he's a "friendly" character, but I sure wasn't impressed or concerned one way or the other.

So, I guess what I'm saying is I'd make substantial changes to the Forerunner and what 343 has done, not to existing character models from the past decade.