Hello! there's already a hotkey for that: select everything you want to reparent, then press P (like parent) to reparent it to a new bone.
Here's the cheat sheet: Spine: Cheat Sheet

The existing way to do this works like this:

1. N
2. click to the parent bone
3. Draw the new bone
4. give it a name.
5. V or any other tool that allows multiple-bone selection. (this step can be really disorienting if you do intend to group several bones)
6. Select the bones or slots you want.
7. P
8. click to select the new parent.

That's not quite the same as what notme1611 was looking for.
I suggested this before though. It would've come in handy pretty frequently for me before.

The functionality:
Create a new parent bone for the currently selected bones... (or slots).
That new bone's parent is the original parent of the selected bone (or slot).

This is helpful for when you want a slot to move on its own independent from the other slots under its parent bone.
Or have one or many bones have a new parent for specific movements on a different pivot.

I agree that just having a keyboard shortcut like CTRL+G just for this function would really help not break flow, especially when you just need to achieve that independent motion or new pivot in the middle of animating.

If we semantically define the feature as "group selected bones under a new bone", then CTRL+G makes sense as a keyboard shortcut.

Probably how to use it:

1. select bones or slots
2. CTRL+G
3. draw the new bone.
4. give it a name

In the case where the selection does not share the same parent, the parent can be chosen according to the parent of the first selected bone or slot.

I think this would also make for an additional intuitive way to first set up the skeleton from the initial Photoshop script json output.

The hold CTRL, select stuff, Create Bone way can be a bit of a pain depending on how images are laid out. (I also realized it doesn't work when you select the slots using the tree instead of through the viewport)

I think folding this feature into the existing "create bone for selected slots" workflow of the Create Bone tool doesn't quite work because your selection is a singular bone, and the Create Bone tool only allows selecting a single bone, which it treats as the parent. I think just allowing a selection of bones for Create Bone causes the same terribly unintuitive ambiguity you'd see in Blender where there's sort of a "primary" selection in a large selection but it's not immediately clear which one or how you set this.

Meaby it will help you a bit but I use scrouts from RTS games. You chose for example face bones and click CTRL + 1. That group selected bones under the 1 button. When you click it, all bones in this group will be selected. You can do groups from 1-0 in fact.
This what really help me and giving me a flow is put CTRL+1 for example to the Root bone and then I create new bone connected to it. After create I click only 1 button to select root and can create next bone parented to the root. Flow is much better
Enjoy!

You're talking about stored selection groups.
notme1611 is talking about modifying the skeleton hierarchy.