A legitimate revalue process would typically obliterate the original value. If anything, this is more consistent with a surcharge to add value and make a 3 cent stamp. Along those lines this is from the era of the WWI postal tax when letters went from 2 cent to 3 cents between November 2, 1917 and June 30, 1919 - and this is more likely a privately applied protest statement of the war tax with no legitimate postal validity. One could make these today with an old type kit.
Oddly enough, this is similar to Canada MR3-MR7 war tax stamps with the tax value added to the postal value.