Hi Terry,
Currently you can't change images on buttons, the issue why it is not too easy to implement this currently is because the functions which upload the buttons and other GUI primitives do not give a unique ID for the elements. So, there is currently no way to refer to an object from a function call. The object is uploaded, but the software does not have a "handle" for it.
In the screen editor when you select the image with clicking then the software checks the active tab page number and then check your click coordinates and then it compares to an array list of items to see what is under your clicked point on the active tab page, so basicly then it searches for the item, but you can't tell the software that I want to select an item without having a unique ID, a handle to it, because you can't refer to your object.
What would be implementable without having that mentioned handle is to change the image on all buttons which has a defined buttonnumber,
I mean for example to change the image on all buttons which for example has the ID 128.
This would be possible because then you could tell the software with a function parameter to change the image on all buttons which has for example ID:128,
because that information is stored and can be searched for in the buttons array list.
The question is would it be enough for what you want to do?