How to change the root bone in Blender
To change the root bone in Blender, create a new bone and parent the original bones to the new bone.
Select the armature, go into edit mode, and we'll extrude one from here. It doesn't have to be there, it can be anywhere on the armature. E to extrude, X for the axis.
Select the bone, Alt P, clear parent, drag it to new location, rotate it upright, select the original root bone, shift select the new bone, Ctrl P, connect it.
And there you have a new root bone.