Rigged model facing the wrong way

I’m trying to import an animated mesh into unity, but the mesh was facing the negative X axis when it was rigged and animated.

Is there any way, or any program to rotate the mesh and all of it’s animations by 90 degrees to have it facing forward again?

Basically, what I would need to do, is to be able to export my FBX from 3ds max with Negative-X forward, the same way one would export as Y-Up or Z-Up

You could try parenting the whole rig and rotating that parent (aka link). But you need to make sure either you retarget* the animation to a simpler rig (without the extra parent) or export out the subset of the rig.

*To retarget a rig you need to create a shadow version of the original rig and ‘constrain’ it to the original adjusted rig.