I don't agree with this - if you set it or override it here, then the tests become much harder to read and/or debug if necessary - you have to hold in your head the original input file, the change, and what is being tested. When there is a potential bug, the bug could be in the input file, in the code you've written to override the input settings in the test or the code itself.

I definitely agree with your above point though - confirm the data is as you expect before embarking on testing.