It can be very hard to get commercial-raised adult birds to switch to a new diet. Just recently I bought a handful of layers at point of lay from a hatchery, and found that they wouldn't attempt to eat any of the home mix. Over a few days they gradually took a little of it, but I would say they were eating about half a normal amount of feed for the first two weeks, and as a result laying was greatly delayed.
The prevailing advice is to do a half-half mix for a week to gradually change birds over to a new feed. However I didn't want to buy a bag of layer pellets just to do a one-week withdrawal to a new feed. Besides, my other birds do well on varying feed.
Accepting variety is a vital part of keeping birds healthy on a home mix. There are times when an important ingredient becomes unavailable (recently I couldn't buy yeast) and so other ingredients need to be added to make up for whatever vitamins are going to be missing. There may also be times when an available feed is of poor quality. And of course price sometimes dictates a change. As a result the home feed isn't a fixed diet but a constantly shifting, constantly changing thing.
The key to being able to vary the feed in this way is to get the chicks used to variety very early on. They have to get used to not only each individual ingredient, but also the fact that the mix itself changes over time. Happily this seems to work.
The only shortcoming is that chicks whose feed includes whole grains etc may be more vulnerable to coccidiosis when the owner is relying on medicated feed (not management) to keep parasite numbers low. If you add non medicated ingredients to a chick's diet, you reduce the amount of coccidiostat each bird eats. Not everyone may be interested in reducing reliance on medications. In that case I would suggest only adding a very small amount of extra feeds, e.g. by way of an afternoon 'treat'.
In the meantime rest assured, when birds are weaned off medications they can still be introduced to a varying natural diet, though the process takes time. My new layers are now eating the mix quite happily, and three out of four are laying (the other is taking a break until the day length increases).