You can read what they actually said about this here (see the paragraph in italics):
Some people with standard install locations had to reinstall, some didn’t. A few people with custom install locations had to reinstall too (but seemed like a very small number and there seemded to be links to how/when they chose to exit the beta) - most who were on custom install locations had no isues.
It’s pretty easy to move the sim to another drive/location if you have one, without needing to reinstall everything. There are many posts in the forum covering this - so if you are worried, you can do this before the beta.