Final answer:
The least appropriate guideline for permanent waving is to ignore the hair's pre-existing condition since this process chemically alters disulfide bonds, which can severely impact previously damaged or treated hair.
Step-by-step explanation:
The least appropriate guideline in terms of permanent waving would be to ignore the hair's pre-existing condition. The process of permanent waving involves breaking and reforming the hair's disulfide bonds. This is initially accomplished by applying a basic reducing substance such as ammonium thioglycolate to the hair. Following this, a neutralizer is used to reform the disulfide bonds, giving hair its new shape. The condition of the hair prior to this chemical treatment is crucial as damaged or previously treated hair can react differently or be further damaged by a permanent waving procedure.
When discussing temporary waving, it is important to understand that the inclusion of water molecules disrupts the hydrogen bonds which are different from the disulfide bonds affected in a permanent wave. As the hair dries, new hydrogen bonds form to create a temporarily changed shape.
Given the chemical nature of permanent waving and its potential to harm the hair if done incorrectly, it's vital to properly assess the hair's condition before proceeding with a permanent wave. Therefore, not considering the hair's pre-existing condition is the least appropriate guideline in a permanent waving process.