It's currently only possible to import new test cases so you won't be able to update test cases via CSV, but you can use the API to post results in bulk. The API versions are linked below.
But another option you might find useful is to update test results in this way,
1. Choose your sort order that's most relevant to what you want to update
2, Click on the cog
3. Choose the status you want to apply to all tests below. I haven't checked but I believe the update will apply to the group of tests below, i.e. not all tests, just those that are in the Group selected in action #1 above
APIs depending which version of Scale you're using: