There are two different questions. 1) Do I need to correct my DA/MDA 2) Am I allowed to follow the vertical path and related LNAV/VNAV minima.
To answer question 1. --> Every time the temperature drops below 0, the DA/MDA needs to be corrected. My company uses 10% of the height, to be added to the DA/MDA. So if the minima is 400'(300), where the height is in brackets, the new minima becomes 400' plus 10% of 300' --> 430'*.
The second question depends on the equipment that you have on board. On some airplanes you'll have temperature compensated systems, like FLS on some Airbuses. If you do NOT have temperature compensated equipment, you can only follow the vertical path until the published temperature on the chart, or 0ºC. In your example the published temperature is -20º, so you're authorized to follow the vertical guidance down to LNAV/VNAV minima (but these need to be corrected, see question 1).