Yes, you can. 100% This is actually something in the Canon ecosystem that predates the 5D4. I have the same setup on my 7D2. Look on page 502 of the 5D4 user manual:
: Switch to registered AF function
Only while you hold down the depth-of-field preview button or the lens’s AF stop button, you can apply AF with the following settings: AF area selection mode (p.104), Tracking sensitivity (p.132), Acceleration/ deceleration tracking (p.133), AF point auto switching (p.134), Servo 1st image priority (p.136), and Servo 2nd image priority (p.137). Useful when you want to change the AF characteristics during AI Servo AF.
*2: Onthesettingscreen,pressthe<B>buttonto display the detailed settings screen. Turn the <5> or <6> dial to select the function to be registered, then press <0> to add a checkmark [X]. When you select a function and press <0>, you can adjust the setting. By pressing the <L> button, you can revert the settings to their defaults.
(Sorry, this didn't copy/paste well)
So again, you can set up your * or AF-ON for one shot or AI SERVO with say, 1 single point or 5 point expansion or whatever. Then you can program the DOF preview button for an entirely different set of characteristics that involve all or some of the available settings. I have mine set to keep the same AF characteristics except the AF selection which I have set to a larger AF selection area. And again, you can customize your * and AF-ON in combination with your DOF preview differently for each custom setting dial position (C1, C2, C3) as well as generally for the advanced shooting modes so you'll be able to program more customs AF functions than you're likely to remember. When shooting wildlife it is extremely valuable to be able to track something in AI SERVO while having the ability to move between completely different sets of AF characteristics seamlessly.
Thank you very much for taking the time to explain this. I'll take another look today and see if I can implement. It's pretty daunting trying to keep in mind everything you can customize!
EDIT: yep, totally awesome, just changed the function of my DOF button to switch to Large Zone AF. Really cool, best tip I've learned in a while.