It is expected that an «allocate» relationship between model elements is a precursor to a more concrete relationship between the elements, their properties, operations, attributes, or sub-classes. Source OMG Systems Modeling Language (SysML) 1.6
If it has isUnmarshall=true, then it must have result OutputPins corresponding to each of the attributes of the Signal of the SignalEvent (in order), and the attribute values of the Signal instance associated with an accepted SignalEvent occurrence ... Source Unified Modeling Language 2.5.1
The Signal trigger simulator in Cameo Simulation Toolkit 19SP3 does not support run-time user-defined attribute values (but you can define defaults)