Since TiddlyWiki Version 5.1.16, it's possible to apply customs styles with data- attributes. see: How to apply custom styles

The Custom data-styles stylesheet tiddler contains the following definition:

[data-tags*="example-hardlinebreaks"] .tc-tiddler-body {
  word-break: normal; 
  word-wrap: break-word;
  white-space: pre-wrap;
}

If rendered without the tag, the content of "Hard Linebreaks with CSS - Example" will be shown like this:

The following text is rendered without any special WikiText syntax. So most of the WikiText functionality will be accessible. This is a line and this is a new line while this is yet another line and this is the final one apart from this one

Open the tiddler to see the custom CSS rules applied: Hard Linebreaks with CSS - Example