In Linux, one can do any kind of adjustments on one's keyboard layout. You don't necessarily need a keyboard layout. You can simply modify your existing xkb keyboard layout.

The xkb keyboard layout files are kept in directory /usr/share/X11/xkb/symbols/. From there just select your language with the code, for instance fr for french, es for spanish, or us for US english.

In that file, all the characters are mapped to keys. Each line in the keyboard is denoted with a code. The line where you have all the numbers is denoted with AE and the keys on it with numbers. Thus the number "1" key is 2nd key on the AE line, thus its code is AE01. On the line, the first symbol you get with pressing the key without any modifiers. The second symbol you get with Shift+key, the 3rd you get with AltGr+key, and the fourth one AltGr+Shift+key.

key <AE01> { [ 1, exclam, NoSymbol, exclamdown ] };

Here you can assign & modify your keyboard the way you find suitable to your needs.

I have couple of modifications, and find them very useful :)

For more info:
https://help.ubuntu.com/community/Howto%3A%20Custom%20keyboard%20layout%20definitions