ArcGIS Desktop - Need to set Merge Rules in Spatial Join for 90 fields, is there a way to do this in bulk? Change default merge rule?

[MalekSraj]

I am trying to perform a spatial join that will aggregate about 90 fields using a SUM function.

In the Field Map I get the option to right click on each field and set the merge rule to SUM.

This would be extremely tedious for me to do, especially since I have to perform such a spatial join for 30+ layers.

Is there a way to change the "default" merge rule option to SUM instead of FIRST? How about change the field merge rules in bulk?

Below a screenshot of the fields in spatial join that I'm trying to aggregate, I would need to click through each of these and set the merge rule:

[JayantaPoddar · Accepted solution]

Have a look at fieldmap.mergeRule parameter in the Python Script in Spatial Join—Help | ArcGIS Desktop 

[MalekSraj]

Thanks, isn't there a way to do it without ArcPy?

[DanPatterson_Retired]

The link Jayanta provided is for the spatial join tool in ArcToolbox... why not use it? He was pointing out the options and what they mean.