GSFont replaceObjectInInstancesAtIndex:withObject:

func replaceInstance(
    at idx: UInt,
    with instance: GSInstance
)

- (void) replaceObjectInInstancesAtIndex:(NSUInteger) idx
                              withObject:(GSInstance *) instance;

replaceObjectInInstancesAtIndex_withObject_(
    idx: int,
    instance: GSInstance
)

instances
Export configurations of the font.
countOfInstancescountOfInstances
The number of instances in the font.
objectInInstancesAtIndex:objectInInstancesAtIndex_
Returns the instance at an index, or nil when the index is out of range.
insertObject:inInstancesAtIndex:insertObject_inInstancesAtIndex_
Inserts an instance at an index.
insertInstance:atIndex:insertInstance_atIndex_
Inserts an instance at an index.
addInstance:addInstance_
Adds an instance to the font.
addInstanceFast:addInstanceFast_
Adds an instance without undo registration or change notifications.
removeInstance:removeInstance_
Removes an instance from the font.
removeInstances:removeInstances_
Removes instances from the font.
removeObjectFromInstancesAtIndex:removeObjectFromInstancesAtIndex_
Removes the instance at an index.
instanceGroupsinstanceGroups
Instance groups for UI presentation.
instancesUniqueinstancesUnique
Instances with unique interpolation locations.
instanceAtPosition:instanceAtPosition_
Returns the instance at an internal design-space position.
instanceNearestToPosition:distance:instanceNearestToPosition_distance_
Returns the instance nearest to an internal design-space position.

replaceInstance(at:with:)replaceObjectInInstancesAtIndex:withObject:replaceObjectInInstancesAtIndex_withObject_