It depends. If you edit content, your personalizations remain intact. If you delete elements, it might delete your personalizations. More.
Personalizations are like an additional layer of information that is sent to your website visitors. The difference between the personalized web page and the original one is described by a delta (or a diff). Every time you adjust content through Unless, a new delta is created. When someone visits your website, Unless sends out the delta for all applicable personalizations and replaces the original content.
So technically speaking, a personalization is just a group of content changes on top of your original page. It is not a separate, new page.
In general, changing the original page will not "break" your personalizations. However, you might lose certain personalizations in the process since the delta does not apply anymore.
This only applies when you change the structure of your original web page, not the content. So, updating text or images will have no effect on your personalizations, however, deleting elements, will mean losing the personalizations within those deleted elements.
Let's say the headline of your original page is "Unique Bouquets for Mother's Day". Next, you create an Unless personalization and change the headline. So far, everything will work smoothly.
However, your colleague decides to delete the headline of your original page entirely.
Now, the following happens: Since your colleague removed the headline, the delta describing a personalization for that headline will not apply anymore. The headline is gone - there is nowhere to "dock" for the delta. So, the personalization is lost.