English to Chinese Tech/Engineering Energy / Power Generation 现场测试

When equipment is not commercially available or fails to meet performance requirements, modification or alteration of pre-existing equipment designs shall be preferable to the invention of new equipment, unless acquisition and life-cycle cost prove otherwise. 如果设备为非市售设备或不能满足性能要求，则修改或变更原先的设备设计对新设备的制造应是可取的，除非收购和生命周期成本证明不是这样。
unless acquisition and life-cycle cost prove otherwise 不是很理解。