Reverse/change transition on Previous button

No easy way to achieve a reversed transition alas. Phil's solution is probably the easiest one. Another option is creating a transition with GSAP and javascript. That would be easily reversible as you can use timelines with built-in functionality to reverse it. In fact that is quite easy... biggest problem is for push or cover transitions you would need the graphical look and feel of the next and previous slides in the current one...so you can make it look like a transition on the current page.

Moving the currentview... well thats the easy part..

let player = GetPlayer();
var tl = gsap.timeline({onComplete:readyAction});

let slideContainer = document.querySelector("#slide > main");
tl.to(slideContainer, {x: '100vw', duration: 1});

function readyAction(){
console.log("timeline ready!");
player.SetVar("isTransitionDone","2")
}

The code uphere just does that...moving the actual content out of view to the right.
Now figuring out how to get the next page to show properly..