[Phanx]

Here's a version that will use your CVar setting instead, as suggested by Semlar. I also converted the growing if-else chain into an easier-to-maintain indexed table loop:

local shorts = {
	{ 1e10, 1e9, "%.0fb" }, --  10b+ as  12b
	{  1e9, 1e9, "%.1fb" }, --   1b+ as 8.3b
	{  1e7, 1e6, "%.0fm" }, --  10m+ as  14m
	{  1e6, 1e6, "%.1fm" }, --   1m+ as 7.4m
	{  1e5, 1e3, "%.0fk" }, -- 100k+ as 840k
	{  1e3, 1e3, "%.1fk" }, --   1k+ as 2.5k
	{    0,   1,    "%d" }, -- < 1k  as  974
}
for i = 1, #shorts do
	shorts[i][4] = shorts[i][3] .. " (%.0f%%)"
end

hooksecurefunc("TextStatusBar_UpdateTextStringWithValues", function(statusBar, fontString, value, valueMin, valueMax)
	local style = GetCVar("statusTextDisplay")
	if style == "PERCENT" then
		return fontString:SetFormattedText("%.0f%%", value / valueMax * 100)
	end
	for i = 1, #shorts do
		local t = shorts[i]
		if value >= t[1] then
			return style == "BOTH"
				and fontString:SetFormattedText(t[4], value / t[2], value / valueMax * 100)
				or  fontString:SetFormattedText(t[3], value / t[2])
		end
	end
end)