Definitely agree... do not mix feed with treats, seeds, scratch or anything else. Layer feed is specially formulated to offer all the nutrients chickens need to stay healthy. Treats should only be offered sparingly. That can be really difficult to do! It's so much fun to watch them be happy and gobble everything up.
As a general rule, treats (including fruits & veggie scraps) should only be 10% of their total feed ration. An average chicken eats about ¼ lb. per day. If you have 6 birds, and they eat 1.5 lbs per day, total treats shouldn't exceed 2.5 ounces. That's just a guideline, and the mealworms and seeds you've added aren't unhealthy, so they'll be fine. What you really want to avoid is fattening dinner leftovers. My chickens used to have access to my compost pile that frequently had bread, pasta and all manner of scraps. After a year, one bird suddenly became despondent and died. I suspected egg peritonitis so I did a partial necropsy myself, but what I found was an inch thick layer of visceral fat. I think she died from being obese and resulting heart failure, and she was the one who always ate the carbs first, while other ate the fruit/veggies first. So now I'm very diligent about what they get for treats.
My chickens also like to hang out on my back door. They squawk and follow me around looking for treats all the time! But when they're hungry they go back and eat their regular food. As long as you ignore them, they'll eventually learn you're not an automatic treat dispenser. Save your party mixes for training your chickens when you actually want them to come to you or other fun things. In the winter months, you can always throw out a handful of scratch in the evenings right before they roost. Some people do this the help their chickens burn more calories and stay warm while they sleep.