A greasemonkey userscript (for niu.moe, but you just need to change the @include to switch that bit up) to add a "see more" arrow to statuses.

seemoremastodon.js

// ==UserScript==
// @name     See More Mastodon
// @version  1
// @grant    none
// @include  https://niu.moe/*
// ==/UserScript==

function addGlobalStyle(css) {
    var head, style;
    head = document.getElementsByTagName('head')[0];
    if (!head) { return; }
    style = document.createElement('style');
    style.type = 'text/css';
    style.innerHTML = css;
    head.appendChild(style);
}

addGlobalStyle(`
.status > .status__action-bar::before {
	content: "▼";
	padding-bottom: 5px;
	font-size: 15px;
	margin-left: 10px;
	margin-right: 18px;
  color:#606984
}

.greasyshow > .status__action-bar::before {
	content: "▲";
}

.status > .status__content {
	max-height:110px;
}

.greasyshow > .status__content {
	max-height:200%;
}
`);

document.onclick = function(e) {
	var el=document.elementFromPoint(e.clientX, e.clientY);
	if(el.classList.contains("status__action-bar")){
		var par = el.parentElement;
		if(par.classList.contains("greasyshow")){
			par.classList.remove("greasyshow");
		}else{
			par.classList.add("greasyshow");
		}
	}
};