The filter IDs are not subsequent because it would prevent me from adding new filters without breaking backwards compatibility. That's why the FilterModeList object is there. Basically you create a custom array containing all filters you need and add get the correct filter ID via this code:
const var modes = Engine.getFilterModeList();
const var myFunkyFilters = [modes.LowPass,
modes.StateVariableNotch];
comboBox.addItem("LowPass");
comboBox.addItem("Notch Funky Yeah");
inline function onComboBoxControl(component, value)
{
local filterIndex = value - 1;
filter.setAttribute(filter.Mode, myFunkyFilters[filterIndex]);
}
Protip: If you type modes. and press Escape you get a dropdown with all filter modes available.