A script to assign brush presets to any of ten configurable hotkeys.
Go to Tools → Scripts → Ten Brushes.
A Window will pop up with a preset chooser and ten boxes above it. Underneath the boxes is the hotkey the box is associated with.
Select a preset from the chooser and click one of the ten boxes to set it.
To change the associated hotkey, go to Settings → Configure Krita → Keyboard Shortcuts and then change the Activate Brush Preset actions under Ten Brushes
When done, open a file, and press your hotkeys to switch to that preset!