hi 2 all, ,,,my littel booklet states that the plants" nutritional requirements change slowly over the first 3 weeks of the bloom period." hydrotops is designed 2 be mixed(grow and bloom) 4 the first 3 weeks of budding. so if the pants needs change slowly shudent the nutes change over slowly, it doz sound logic 2 me,

yeah, it does sound like a decent argument. There has been a discussion about other nutrients (ionic specifically) causing problems with Mg lockout when flowering, and a way around that was to make up the nutes with 25% grow as well as the bloom.
Its going to depend on what you are using at the end of the day. You introduce more Nitrogen to the plant and its gonna get taller. Its up to you if you want to do that. It may prevent deficiencies later on in the plants life tho.
If your plants do not show deficiencies, esp with a 2 part solution like Canna, then I would not mess with it, and there could end up being a big nutrient imbalance. You have no idea how much of what you are adding after all.
Maybe the nutrient companies need to look at an intermediate nutrient for preflowering (great, more chemicals to buy!)