Sorry, the list indentations are currently hard-coded and
can't be customized.
You could, however, postprocess the docx produced by pandoc,
changing the file numbering.xml in the docx container.
Or you could modify the source code and recompile. These
values are set in src/Text/Pandoc/Writers/Docx.hs at lines
744-5 (step = 720, hang = 480).