You should be able to use your own shortcuts by using the keytip
attribute in the customUI XML for the ribbon, but sometimes the Office programs decide to change it to Y1, Y2 etc., possibly because of a conflict with keytips for the built-in controls.
I don't have Outlook, but I tried the "CKS" keytip in Excel 2010, both on a tab and on a button, and it worked. Below is the XML used for the Excel ribbon:
<customUI onLoad="RibbonLoad"
xmlns="http://schemas.microsoft.com/office/2009/07/customui">
<ribbon>
<tabs>
<tab id="tabTest"
label="Test"
keytip="CKS" >
<group id="grpTest"
label="Group #1" >
<button id="btn1"
label="Button #1"
size="large"
keytip="CKS" />
</group>
</tab>
</tabs>
</ribbon>
</customUI>
keytip
attribute in the customUI XML for the ribbon, but sometimes the Office programs decide to change it to Y1, Y2 etc, possibly because of a conflict with keytips for the built-in controls. – TurpentineCKS
keytip in Excel 2010 (I don't have Outlook) on both a tab and a button, and they both work perfectly... :) – Turpentine