The post you are quoting is from late 2009. It is in reference to TCM V4 where Dimensions was a menu item. Dimension has now been moved to the Inspector palette but the principle is still the same. After creating a new standard and clicking done, return to the Standards dropdown and select your new standard to make it active. If you have assigned this standard to an existing dimension then right click on it and in the popup menu click on "Make Default". Otherwise, make a dimension, right click and set default.
Custom standards are now saved in the program for use in other drawings in the StdDim.ini file. Library -> Application Support -> com.imsi.turbocadmacpro9ESD.