This is the easiest to implement but the hardest to achieve if the change is detrimental. Reducing staff pay rates is never going to be popular. Explaining the necessity for the business to reduce costs and the possible alternatives of redundancy or insolvency will help staff to understand your reasoning. If you can offer a sweetener such as an additional day off or reduced hours it may help to soften the blow and reduce bad feeling.
This where you say what you intend to do and go ahead and do it. You should ensure that you can justify your decision before embarking on any changes. By explaining to staff your reasons and listening to their concerns you may limit the extent of claims including unlawful deduction of wages, breach of contract and constructive dismissal. Take care if applying the changes to one group of employees you could fall foul of indirect discrimination. E.g. if that group of employees were all female.