Skin Framework allows multiple skins to be applied to the same application. You can even apply a different skin style to each individual control on the same form. This allows complete control over how an application is skinned. You might like the buttons from one skin better than another so you can easily apply that skin only to those buttons. Components can also be excluded from skinning if desired.
The picture below shows the main application using a different theme from the popped up dialog. Each button on the dialog is using a different theme.