Relatedly, some aliases I have in place.

  assume = update-index --assume-unchanged
  unassume = update-index --no-assume-unchanged
  assumed = "!git ls-files -v | grep ^h | cut -c 3-"
  unassumeall = "!git assumed | xargs git update-index --no-assume-unchanged"
  assumeall = "!git st -s | awk {'print $2'} | xargs git assume"