The following sets round corners globally
@startuml
skinparam roundcorner 20
participant Test
@enduml
Ideally I would like to be able to set both round and diagonal corners per stereotype, e.g.
@startuml
skinparam participant {
BackgroundColor<< number1 >> #GoldenRod
DiagonalCorner<< number 1>> 20
BackgroundColor<< number2 >> #Green
RoundCorner<< number2 >> 20
}
participant Test
participant Test1 <<number1>>
participant Test2 <<number2>>
@enduml