End User will not know if any stage is alternate. It is up to you to configure as a alternate stage. Just conventionalize the the change stage activity, call it when required so that the work item is moved to Audit. In the approval stage, create a step to update status of the work item. skip the step when the stage is changed. add the update status step in the audit stage also.

> Since the majority of the cases are required to go through the "audit" stage, having alternate "audit" stage is conceptually incorrect and unlikely to be accepted by end user. 

Chunzhi Hong, If the audit is part of the normal path you are correct, i'd define it as a regular step and put a "start when" condition on it.

However Audits are usually the bottle necks in a process and consume a lot of man power. By putting rules that will score the work to be reviewed Pega can detect which case to send to the audit. For instance, in the first version of an expense report application, many cases will be routed to management. then overtime, rules will be added to route only cases that are flagged by the system and the audit will gradually become an exception.