LovebirdLover, have you perhaps thought about taking in these Eclectus and waiting to breed them after you have come to learn and understand these birds? It's very clear you are set on obtaining this breeding pair regardless of what many have advised, and we can all only say so much. I directed you to this species forum because many of the owners her genuinely love their birds and ensure their birds live the best life, as I am sure that is your intention also - however, good intentions don't always turn into good actions.
I do love that you're building a large aviary for them, but you do need to recognize that you are still unsure about their diet despite wanting to breed them - I applaud you for wanting to know, as any good parront would, but I do also recommend that you do not breed these birds until you understand the species. Of course, you won't know anything until you do it, which is what I understand you are trying to say regarding their breeding, but you do need to cover the basics before you try to land a triple back flip off a 50 foot diving board into a 3 meter wide pool (this is my best representation of how steep the learning curve is right now, silly, I know

).
To answer your question about everyday - think about yourself. Do you eat the exact same thing every day? Would you get your required macronutrients and micronutrients doing so? I'm sure you know the answer is no. You can find many lists of bird safe foods, and members have - in detail - explained the diversified diet their Eclectus eat. They have also mentioned organic is better for them ($$$). Varying up their diet every day is what is key, and before even going there, you have to know what they even like. Do they even like mangos? Will they eat kale? Do they like minced parsley or whole parsley? Are they really going to eat that much apple? What kind of lentil mash should I give them today? These are questions you will struggle with daily while trying to feed them properly, so do try your best.
As for switching them over, your birds will, once again, decide that for you. If you remove everything and switch, will they even eat fresh fruits and veggies? Will they turn up their beaks and say no? Will they enjoy it? We don't know. We can't tell you. Your birds will.
As for artificial, you have to be so careful as to not overdose your birds on a vitamin. If they are eating some high quality pellets on top of a very diverse, healthy fresh diet, then no. Supplementing them is likely over kill. Find out the bird safe fruits and veggies (and remember, certain parts of fruits, such as seeds, are POISONOUS) and find out which vitamins they offer. If you find their diet lacking in certain aspects, I'm sure supplementing is fine, but a good avian vet can tell you what vitamins you're lacking based on the diet you're feeding them.
Once again, please do not rely on good intentions to make this a success. I know you only want to experience it, and I applaud that, I do. But what I applaud more is someone making a conscious effort to ensure the longevity of the animal companions in their lives, even if that means taking a step back and saying no to yourself once in awhile, even if it's what you really want. Loving something does not mean you are helping it live a healthy life... look at all the obese cats and dogs in the world. Owners say it's because they love them, but realistically they're killing them slowly but surely, and it's a very, very sad fate for their animals. I hope I haven't offended you but have instead enlightened you, and I do hope you take a few days to reflect on what actions you should take regarding this decision. Remember it doesn't only affect you, but the lives of those birds and their babies, too. Every action has a reaction
