Yes, it is possible, though it will require a bit of working around. Let's say, your family line (correctly) looks like this: "John" -> "William" -> "Daniel" (with Daniel potentially having children or a partner of his own).
If you have accidentally Daniel as John's son and forgotten to add William in-between them, the first step is to just add William as John's son as you normally would. Add his partner (Daniel's mother) as well. Now William and Daniel are displayed as siblings.
Now you select Daniel. On the sidebar, the last button displayed is "More Options". Click on it, and then choose "Set Daniel's parents". Currently, John and his partner (Daniel's grandparents) are displayed as his parents, but now you can change Daniel's father from John to William and do the same with his mother. This will move Daniel and all people associated/descending from him one generation later. (If Daniel has siblings, you'd need to repeat this step for each sibling manually.)
Hope this helps!