Preparing to run before presenting a very hacky solution, have you tried the following?
<code><<span style="display: none"></span>%+ tR = "Completed" %></code>
It actually works, and it’s even possible to copy the entire templater string and it’ll get pasted without the nasty stuff…
As a variant over that theme, you could possibly do a special class for the code element, this is untested but something like:
code.T::before {
content: "<%";
}
And then use:
<code class="T">+ tR = "nicer?" %></code>
(You could potentially use ::after for the ending %> also, if you want to)