This how-to should do the trick for system-wide keyboard remap of single keys: FAQ: How to disable/remap a keyboard key in Linux?
And this how-to is about creating your own custom keymaps: Custom Keyboard Layout in Ubuntu (or just Linux :)
It won't allow you to change it quicky using a shortcut. You'll need some scripting to do so, I guess.
However, from the first revision of your question I assumed you wanted to change layouts. You've revised your question, but here is how to change layouts:
From the tags I assume you're running Kubuntu (KDE) 12.04 changing layouts pretty straightforward:
- Open 'System Settings'
- Open 'Input Devices'
- Select 'Keyboard' on the left vertical tab.
- Select 'Layouts' on the horizontal tab.
- Tick the checkbox 'Configure layouts'.
- Add your preferred keyboard layouts by clickin the 'Add' button and filling in the fields in the dialog. Selecting an English (US) layout will result in 'qwerty'. -- Optionally configure a shortcut key to change layouts quickly.
- Click apply.
This should cover keyboard layout and behaviour in your user session. For system wide settings including text console, see this question.