[Foxlit]

For a more complete change-spell-on-state example:

 local sBtn = CreateFrame("Button", nil, UIParent, "SecureActionButtonTemplate"); -- [1]
 parentHeader:SetAttribute("addchild", sBtn); -- [2]
 sBtn:SetAttribute("statebutton", "1:state1;2:state2;3:state3"); -- [3]

 local spells = {"Immolation Trap", "Frost Trap", "Snake Trap"};
 sBtn:SetAttribute("type", "spell"); -- [4]
 for i=1,#spells do
  sBtn:SetAttribute("*spell-state"..i, spells[i]); -- [5]
 end

1. Create a SecureActionButton to do things with. There's no skin included here -- you'd need to add your own textures, dimensions and anchors to actually see the action button.
2. parentHeader is the SecureStateHeader whose state this button will alter behavior based on. Setting the "addchild" attribute on a SecureStateHeader fires its SecureStateHeader_OnAttributeChanged, which applies the necessary changes to the child -- like replacing the child's OnClick handler with SecureStateChild_OnClick.
3. This attribute makes SecureStateChild_OnClick change the button attribute passed to SecureActionButton_OnClick (the default OnClick handler for a SecureActionButton) based on the header's state. In this case, if the header is in state 1, the SAB thinks the button "state1" was used to click it; same with "state2" in state 2 and "state3" in state 3. The attribute's general syntax is "state:newbuttonstring;otherstatetherbuttonstring;...".
4. All three actions are spells, so we do not have to bother with modifying the "type" attribute based on anything.
5. Both "type" and "spell" attributes are retrieved using SecureButton_GetModifiedAttribute. So, in this attribute's name ("*spell-state{i}", where {i} is replaced by numbers 1 to 3 depending on the iteration of the for loop):
   • "*" prefix enables all modifier combinations.
   • "spell" is the actual unmodified attribute name.
   • "-state{i}" is the button this attribute is valid for. The state1, state2, state3 buttons are the result of the "statebutton" attribute set above.