You can definitely get away with more if you enter the park prior to HHN and stay in a holding area than you can if you enter after HHN has begun.
My understanding as to why security is ramped up for HHN is essentially: Drunk Adults + People Jumping out and Scaring Them = Potential for Volatile and Violent situations to break out, endangering both guests and park employees. Are fights rampant or anything? No. But I'm sure they see their fair share in a season, so they crack down extra hard on anything that could potentially be a weapon.
As an example, I attended 2 nights at HHN 15 in 2005 (and I'm going to preface this by saying: in 2005, park screening standards were way more lax in general). As a teen who couldn't even legally drink at the time, I wore a chain attached from my belt to my wallet. The first night I stayed in a holding area, the wallet chain was no problem. I wore it into the park during the day, in and our of the holding area, and no one cared or said anything when things rolled over into HHN.
The second night, I didn't stay in a holding area, and entered HHN later, and they refused me entry w/ the chain. I had to check it in at the front of the park and pick it up at the end of the night before they'd let me enter, despite no one having a problem with it the night before.
By TODAY'S Screening standards, they might not even let you in during the day with a wallet chain, frankly. Florida parks have gotten way more crotchety about "potential weapons" (I don't personally know however, as I stopped wearing it around my late teens, so it's no longer an issue for me). But regardless... if you're trying to get away with anything, you're better off doing it during the day and staying in a pen. Because once HHN starts they're extra picky.
True Story: My HHN Trip is in Sept and my Vegan friend wants to smuggle in cooked Potatoes in a Fanny Pack for herself to snack on. I plan to warn her of all this, because I honestly feel they might view Potatoes as a snack during the day, and as a potential projectiles after HHN starts.