Wai,
Unfortunately, you cannot dynamically change the image set used by a DirectSmile object.
You could, of course, create multiple layouts, each with a different DirectSmile set, and put conditions on the layouts so that it chooses the correct layout for every records. This will work well if you have a small amount of sets available, and it's always alternating between them.
However, if you have thousands of sets, then obviously this isn't a very good approach due to the amount of layouts that would need to be created and maintained. If that's your case, then unfortunately, there may not be much we can do.
Regards,
Raphaël Lalonde Lefebvre