As Erik mentioned it might be a bit overkill to it per cell basis?
Either way have a look at the Generic Object Definition documentation as it contains all the properties that can be set.
For example, your extension can have more than 1 hypercube definition, your hypercube can also contain self-contained expressions (useful for stdev calculations for example).
In this case I guess that you could use what we call Attribute Expressions, similar to how colors can be defined per row value. It's an extra expression associated with your measure.
You can find the definition here https://help.qlik.com/sense/en-us/developer/index.html#../Subsystems/EngineAPI/Content/GenericObject/PropertyLevel/Hyper…
Sorry for late answer, thanks for your answers.
My intent is to get an expression evaluated for each hypercube row (not cell).
How can I modify Hypercube definition directlly from property panel ? If someone can post some code example for setting an additionnal self-contained expression, it would be usefull.
I found this trick to get it working...
type : 'string',
label : 'Evaluates for each row',
ref : 'qAttributeExpressions.0.qExpression',
You'll find more details in this post : Qliksense custom measure property for extension with expression value