[Is there a formal way to set/get/clear _gsTransform?]

Sure, if you want to clear those, you can do something like this:

TweenLite.set(element, {clearProps:"transform"}); 

It'll also work if you clearProps: any transform-related value, like clearProps:"rotation". 

 

 

 

apparently clearProps deletes previously set (inline) transform properties of an element...

is there a way to revert back to element's original inline styles? 

 

HTML:

<div id="el" style="-webkit-transform: rotate(45deg);">blabla</div>

JS - tween:

TweenMax.to("#el", 2, {rotation:125});

JS - clearProps:

TweenMax.killTweensOf("#el");
TweenMax.set("#el", {clearProps: "transform"});

the result is not as expected, element rotation is at 0 degrees instead of 45 degrees