<p>Is possible to insert a line break where the cursor is in Vim without entering into insert mode? Here's an example (<code>[x]</code> means cursor is on <code>x</code>):</p>

<pre><code>if (some_condition) {[ ]return; }
</code></pre>

<p>Occasionally, I might want to enter some more code. So I'd press <kbd>i</kbd> to get into insert mode, press <kbd>Enter</kbd> to insert the line break and then delete the extra space. Next, I'd enter normal mode and position the cursor before the closing brace and then do the same thing to get it on its own line.</p>

<p>I've been doing this a while, but there's surely a better way to do it?</p>

For the example you've given, you could use
r
Enter
to replace a single character (the space) with Enter. Then,
f
space
.
to move forward to the next space and repeat the last command.
Depending on your autoindent settings, the above may or may not indent the return statement properly. If not, then use
s
Enter
Tab
Esc
instead to replace the space with a newline, indent the line, and exit insert mode. You would have to replace the second space with a different command so you couldn't use '.' in this case.