Do you know, that… ?
Variable spacing has long been possible in parts in linear and circular patterns. Such an option has appeared recently in assemblies.
It allows you to select from global instance spacing and change the values locally. After expanding the tab Instances to be replaced click on a given instance and then Modify the instance.
You can now enter the data corresponding to this instance in the parametric values window. This way you can eg. decrease or increase the spacing at a selected location in the pattern. Modified Instances are marked in green and placed in a separate tab.