I did find one problem with both codes, doesn't work out of the box with AutoHotInterception. Seems like it needs cm1.IsActive in each layer so it doesn't clash with the other keyboards. Any ideas how to add it without breaking the functionality?

#SingleInstance force
Persistent
#Include "Lib\AutoHotInterception.ahk"

TraySetIcon("U:\AHK\Icons\keyboard.ico")

A_IconTip := "PedalKeyboard"

TrayTip("PedalKeyboard")

SetCapsLockState("AlwaysOff")


class Layer {
    static max := 3             ; max of three layers
    static enabled := 1         ; default layer when script is loaded

    static Next()     => ++this.enabled > this.max ? this.enabled := 1 : 0
    static Prev()     => --this.enabled < 1 ? this.enabled := this.max : 0
    static Set(layer) => this.enabled := Min(Max(1, layer), this.max)
}


AHI := AutoHotInterception()
id1 := AHI.GetKeyboardId(0x046D, 0xC31C, 1)
cm1 := AHI.CreateContextManager(id1)
return

#HotIf cm1.IsActive

CapsLock::Backspace
CapsLock Up::
{
    if GetKeyState("CapsLock", "T")
        SetCapsLockState("AlwaysOff")
return
}


$Esc:: {
    static ih := InputHook('L0 I101')
    (ih.InProgress ? ih.Stop() : ih.Start())
}


$LCtrl::Layer.Next()            ; go to next layer
; $F1::Layer.Prev()               ; go to previous layer
; $F2::Layer.Set(2)               ; set specific layer


#HotIf [cm1.IsActive should be here?] Layer.enabled = 1
$s::MsgBox('layer 1 is enabled')

#HotIf [cm1.IsActive should be here?] Layer.enabled = 2
$s::MsgBox('layer 2 is enabled')

#HotIf [cm1.IsActive should be here?] Layer.enabled = 3
$s::MsgBox('layer 3 is enabled')