It's a good question. I don't believe we have tested this recently enough to give you a clear answer on the likelihood of it "breaking" your layouts- but I can encourage you to experiment in the knowledge that it will be reversible one way or another.
The only part of Design System that could break your Bootstrap 4 layouts is a CSS file. If something wasn't compatible and you wanted to fix it- there are two main ways:
- 1 Fix it- The Design System CSS will be hidden behind the scenes, but would be positioned at the top of the document, so you can override problematic rules with any of your own CSS rules, as long as you are specific enough.
-2 Reverse it- We would be able to remove the link to the CSS for you.
Hope this helps?