Here's a starting point for creating the pictures you want.
shape main
{
layouttype="border";
if(hasproperty("diagram.mdgtype", "ArchiMate3::Application"))
{
AddSubShape("ProcessStep","center");
}
else if(hasproperty("diagram.mdgtype", "BPMN2.0::Business Process"))
{
AddSubShape("Activity","center");
}
else
{
AddSubShape("DiagramType","center");
}
shape ProcessStep
{
ellipse(0,0,100,100);
println("#name#");
}
shape Activity
{
roundrect(0,0,100,100,10,10);
println("#name#");
}
shape DiagramType
{
rectangle(0,0,100,100);
println("#diagram.mdgtype#");
println("#diagram.stereotype#");
println("#diagram.type#");
}
}