What's the modern way of changing the damage numbers' size(I know the colors are from adv.options)?
The way the damage numbers are displayed is dictated by the font used (on your screen HudFontMedium is used for instance). In the ClientScheme.res, fonts are defined with what system font should be use and with what size. So, if you want to alter the size of the damage numbers, you have to change the font used. You can either use an already existing font with a larger size or create one yourself by replicating lines and increasing the number.