What does Scarlet Witch do to the Westview hex barrier in the latest installment of everyone's favorite MCU sitcom, WandaVision? As the Westview anomaly enters the era of big hair and bright pants, several major questions were answered about WandaVision's big mystery. Both Monica Rambeau and Norm (freed from the illusion by a suspicious Vision) reveal that Wanda is the town's puppet master, controlling the physical forms of residents with her magic abilities. Darcy goes further, figuring out that Wanda is rewriting reality, rather than casting an illusion, but in a later conversation with Vision, the Scarlet Witch maintains that she doesn't know how the sitcom started rolling.
Armed with knowledge that the "hex" (Darcy's name for Wanda's Westview reality), transforms real-world objects to fit the sitcom's setting, SWORD send in a rudimentary drone from the 1980s, figuring the barrier won't alter something if it isn't an anachronism. SWORD's drone makes contact with Wanda, but only succeeds in making the Scarlet Witch angry. And just like a certain other Avenger, you wouldn't like Wanda when she's angry. She exits the barrier, crushed drone in hand, tells the assembled agents to back off, and places her hands on the hex, covering the entire field in her trademark red magic. What's going on here?
The immediate assumption is that Wanda reinforces the Westview hex so SWORD can't throw any more outdated weapons through the barrier. Wrapping her red magic around the existing field, no intruders should be able to enter. Originally, the energy surrounding Westview was fluid, allowing Monica to enter and exit, as well as drones and agents in haz-mat suits. But Wanda herself admits that everything she wants is already within Westview. Perhaps, therefore, the hex is now absolute - nothing comes in, and nothing comes out. Alternatively, Wanda may have changed the rules so that instead of only morphing out-of-time objects (such as Monica's bulletproof armor becoming a pair of swinging 1970s pants), absolutely anything that enters the barrier is bent to her will. This measure would also ensure no more interruptions to Wanda's programming. In either case, Wanda changing the barrier would essentially act as a plot device to explain why SWORD can't simply send more 1980s weapons inside, and why they must instead come up with a more creative solution.
Aside from protecting herself from the outside world, Wanda might've also rewritten the rules regarding what happens inside Westview. In episode 5, it's revealed that Scarlet Witch broke into SWORD's base and stole the remains of Vision's body left over from the Battle of Wakanda. Combined with what has already been revealed about Westview, it seems Wanda needs physical bodies to create her sitcom characters (possibly with the exception of Tommy and Billy). It's curious then, that Evan Peters arrives as Quicksilver at the end of the episode. Has Wanda found another random body that wasn't yet given a role? Or has she created another way to bring Pietro to her TV show, either by cracking open the multiverse, or manifesting him from scratch? Wanda's reinforcement of the hex might've been designed to augment her alternate reality even further with new characters.
Since Wanda doesn't know how the Westview anomaly began, there's clearly a deeper story behind how WandaVision was green-lit, but the fact that Scarlet Witch can alter the hex adds further proof to suggest she's the one responsible for the barrier. If the energy field was emanating from another source (Agatha Harkness or Mephisto, for example), Wanda likely couldn't have made any alterations to the hex herself.