Owning a few pet rats when you were younger doesn't make you an expert on the dietary needs of rodents. Rat block of the highest quality is made from non genetically modified corn and is checked for molds and pesticides meticulously. It is SPECIFICALLY crafted to prevent tumors (which is why they use non genetically modified corn and soy) because can you imagine if all the rats in the labs were growing tumors all over the place?
Rat block is scientifically formulated to contain everything a rat will ever need for it's entire life. They don't need vegetables as a supliment. And, as I said, feeding rats too many veggies or fruits will give them gastrointestinal problems such as diarrhea, bloat, constipation, and it can upset the balance of bacteria in the intestines, which can eventually lead to starvation and death.
Treats are acceptable. But feeding on a regular basis is not health for a rat, or most any rodents that I can think of off the top of my head. They are grain and seed eaters, nor herbivores. :)