A dramatic change certainly will harm your fish especially if you are changing the water irregularly instead of consistently however a fish used to frequent water changes, tend to be healthier than those kept in substandard conditions. No point why you have to worry about large frequent water changes if you are quite consistent in its maintenance otherwise take it slow first by pulling out a small portion of the water in the first few days and progressively increase the water volume in the following days. This will give your fish time to adjust well to the changes.
Once a day feeding is fine provided your fish are already adults. Young fish should be fed almost frequently otherwise you risk stunting them in the process as they are unable to gather the proper nutrients in order for them to develop properly. You can still compensate their additional wastes with upgraded filtration systems and frequent water changes.