If there is a file named dviout.par in the dviout directory, dviout reads the parameters from the file when start-up.
If the corresponding Parameters are set "Read" (a "+" mark) in the Property Sheet->[REGISTRY] page, then the parameters are also read from the Windows Registry and overwritten. (If the default is null, then a null value is written.)
To have the parameter file take precedence over the Registry, cancel the aforementioned "Read from Registry" setting, or set the -file: parameter (Property Sheet->[System] page) to the parameter file.