Features used to implement the example

• Write field on issues returned by JQL query or issue list
• Write field on linked issues or sub-tasks

Example: Moving sub-tasks to "Open" status when parent issue moves to "In Progress"

We see provision in JWT to change parent issue's status when a sub-task's status changes. Similarly , is there a way to change a sub-task's status when its' parent issue's status changes? For instance, if parent  issue status changes to "In Progress" , sub-task status change to "Open". 

Yes, you can do it inserting Write field on linked issues or sub-tasks or Write field on issues returned by JQL query or issue list post-function in transition "Start Progress" of parent's workflow. In the case of Write field on issues returned by JQL query or issue list you should use the following configuration: