I've decided to enhance the mechanism os composing keys. With the original Ducky Scripy it is only possible to compose keys with SHIFT, ALT, CONTROL and GUI.
The solution to allow several keys to be pushed is use a flag Hold_Next_Key which simply tells the Ugly interpreter to not send a key release after the next valid key.
With that, the combination keys tokens 0xa8 to 0xab have the same effect that is to set the Hold_Next_Key flag.
With that in mind a GUI R command shall be sent as:
hold gui r 0xAB 0xE3 0x15
Then a CONTROL ALT DEL should be sent as:
hold contol hold alt del 0xAB 0xE0 0xAB 0xE2 0x2A