In the DATEX Tool, you cannot deselect roles with an index qualifier.
The Tool treats them as mandatory. This is because of the 1-1 relation, which determines – in these special cases - in fact the size of the qualified subitems.
I think, in the resulting XSD, this is no problem, the field is not set mandatory.
In fact, there is no change for the modeler to determine, if such aggregations should be optional or mandatory. Maybe this is an methodology issue, too.
Checked what the UML specification says about multiplicity of the population, as opposed to the multiplicity for a specific qualifier value. UML v2.4.1 superstructure says:
"The “raw” multiplicity without the qualifier is assumed to be 0..*. This is not fully general but it is almost always adequate, as a situation in which the raw multiplicity is 1 would best be modeled without a qualifier."
Found bug, now its possible to deselect associations that has a qualifier (always).