How to append custom characters in builtin component

[Nias26]

So, i wanto to append some characters to customize the builtin branch component, but I have no idea on how to do it. Neither the wiki or online pages tell about this.

I've tried something like this:

{
	"(" .. "branch" .. ")",
	icon = "",
	color = { fg = "#767676" },
}

Expected result: (master);
Got: ;

I've tried to make my own component, but neovim lags a lot using vim.fn.system() and io.popen()

Is it possible to do something like this?