I have tried to change the lat long to UTM using "Save As" in QGIS 2.18.13 and tried again in QGIS 3.0.1, I cannot get it to work.
I have a .csv file in the form
id Base_latitude Base_longitude
L001 -33.913912 150.862774
L002 -33.942172 150.857137
L003 -34.055889 150.747552
I then right click on the layer, click "Save As" and set the CRS to ESPG:32756 - WGS 84 / UTM zone 56S and save it as a new .csv.
According to the tutorials and previous stackexchange answers this should produce a .csv file in the form
X Y id Base_latitude Base_longitude
number number L001 -33.913912 150.862774
number number L002 -33.942172 150.857137
number number L003 -34.055889 150.747552
Instead the output .csv is exactly the same as the input. Am I missing a step? I've tried in two different QGIS versions (2.18.13 and 3.0.1) so I don't think it's a bug.