Prevent Python script tool from automatically filling output boxes

I am creating a script tool as part of a Python Toolbox (.pyt) that performs some fairly basic tasks. The tool takes a single input file and creates three output rasters (see image). The problem I am having is that somewhere in Hidden ArcMap World, ArcMap is automatically populating the three output raster paths with the same path when the user gives the single input.

I have attempted to work around this in 2(+) ways.

• by having a check in updateMessages that raises an error if any of the ouputs match path/name
• by trying to automatically generate file names in updateParameters whenever the user has altered the input parameter (and the others dont yet have a "value" or have not been "altered")

How can I either [1] prevent ArcMap from populating parameter names without changing their status to "Optional" or [2] force ArcMap (or arcpy) to use different names when automatically populating those parameters?

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