[Phanx]

1. Add this line to your addon's TOC file:

## SavedVariables: MyCustomTextFormat

2. Modify your addon's Lua code like so:

MyCustomTextFormat = "VALUE"

hooksecurefunc("TextStatusBar_UpdateTextStringWithValues", function(statusBar, fontString, value, valueMin, valueMax)
	local str, val
	if MyCustomTextFormat == "PERCENT" then
		-- Show the value as a percent
		str, val = "%.0f%%", value / valueMax * 100
	elseif value >= 1e10 then
		-- Shorten 10,000,000,000+ like 12b
		str, val = "%.0fb", value / 1e9
	elseif value >= 1e9 then
		-- Shorten 1,000,000,000+ like 8.3b
		str, val = "%.1fb", value / 1e9
	elseif value >= 1e7 then
		-- Shorten 10,000,000+ like 14m
		str, val = "%.1fm", value / 1e6
	elseif value >= 1e6 then
		-- Shorten 1,000,000+ like 7.4m
		str, val = "%.2fm", value / 1e6
	elseif value >= 1e5 then
		-- Shorten 100,000+ like 84k
		str, val = "%.0fk", value / 1e3
	elseif value >= 1e3 then
		-- Shorten 1,000+ like 2.5k
		str, val = "%.1fk", value / 1e3
	else
		-- Don't shorten under 1,000
		str, val = "%d", value
	end
	fontString:SetFormattedText(str, val)
end)

SLASH_CUSTOMSHORTTEXT1 = "/pct"
SlashCmdList.CUSTOMSHORTTEXT = function()
	MyCustomTextFormat = MyCustomTextFormat == "VALUE" and "PERCENT" or "VALUE"
	print("Short text now showing", strlower(MyCustomTextFormat))
end

If you don't want it to remember your preference between reloads or logouts, just skip Step 1.