This is where using a pivot object or pivot limb comes in handy. A pivot object or limb is something that remains in a fixed orientation to which the main object is attached.
For example, let's say you build a human character that you want to back flip. The root limb might be a tiny plane or a tiny triangle. The main character is built attached to this limb. Whenever you position the character in 3d space, you position the root object. When you Y rotate the the character, you Y rotate the root. But whenever you X and Z rotate the character as a whole, you rotate the limb attached to the root (maybe the hips or the body depending on how the character was built.
This will allow you to change the y direction of the character and the world position without there being an influence by the X and Z angles (as long as you don't rotate the root.
A version of this without having the pivot limb built in is using glue object to limb. You would create a plane or a triangle, and Glue the character to limb 0 of the plane or triangle. For example:
load object "human",1
make object plain 2,.001,.001
glue object to limb 1,2,0
Move the plain around and the human will move with it. Steer the plain (yrotate) and the human will steer. Back flip the human by x rotating object 1 (not the plain) as BN2 describes above.
This is a quick solution and will work well most of the time. Gluing though, will interfere with the glued object's collision testing because it's true position is not updated internally when glued. It's rendered (drawn) position is relative to the object it is glued to - but it's absolute position is not updated with the positioning of the pivot object. And if you hide the pivot object, move it, the glued object won't update until the pivot object is visible.
For these reasons, a pivot limb is a better choice, but if you are careful, you can use gluing the object to a pivot.
Enjoy your day.