Usually, if a new employer decides to make contractual changes, this would be classed as a breach of TUPE regulations. The employer would need to prove that the changes are not a direct result of the business transfer.
But, there are scenarios in which contractual changes can be made. Such as, the changes being permitted as part of the contract itself, or due to external factors such as company structure issues, technological issues involving equipment and affecting day-to-day business, or economic influence on company performance.
It’s important to seek legal advice in this instance.