I've done a bit of experimenting....
It seems that you can create a file which contains only the alias portion of the layout and import it to any toon.
So if you first export a toon's layout, then copy only the alias portion, to another file and include the </UI> at the end.
Then import that it will only overwrite the aliases portion of any toon's layout.
a file saved as: ..../UI/Layouts/Aliases.layout
Can be imported by any toon using: /ui layout load Aliases.layout
<?xml version="1.0" encoding="UTF-8" standalone="no" ?>
<Alias String=";hi" Value="shakes his fist at ;target and yells 'Get Off My Lawn!'"/>
<Alias String=";myloc" Value="/tell valalin ;loc"/>
<Alias String=";otg" Value=";tant ;hi"/>
<Alias String=";release" Value="/pet release"/>
<Alias String=";tant" Value="/tantrum"/>
When successfully completed, this load command will display a list of your aliases added. Similar to the "/alias list" command.