Ok, so I can't even get godots IK to work anymore(it used to work though). Don't know why, so I can't even test my ideas out. :(
To be hones though, I don't think godots skeletal/IK system is complex enough to allow doing this. In blender I would create multiple control bone chains and set up a slider or a checkbox/custom property, drivers and constraints, etc. to control the influence and so on to achieve this. Might animationTreePlayer enable doing some of this? perhaps, I have yet to take a look at this.