Does the GetCustomImage method get called when the button is on the Quick Access Toolbar?
If so, then it shouldn't be too hard to do what you're asking. You just need to know if the button is in the Ribbon or the Q.A.T.
BUT
If that does not work, I don't think it's possible to do what you are asking. Each button can only have 1 image and 1 size associated with it.
What you could possibly do is have 2 buttons and toggle which one is visible. And the user could make sure to add the buttonNormal
to the Quick Access Toolbar. I mean, this is ugly and I don't know if I would do this. But if the ugly icon is really bothering you, then go ahead.
<group id="MyGroup">
<button id="buttonLarge" size="large" image="largeImage" label="Test" getVisible="GetIsLargeButtonVisible"/>
<button id="buttonNormal" size="normal" image="normalImage" label="Test" getVisible="GetIsNormalButtonVisible"/>
</group>
And then in the GetIsNormalButtonVisible
and GetIsLargeButtonVisible
methods, you could hide and show whichever one you want.