You can manage (i.e. create, update, delete) Pre-Conditions directly through the JIRA's native REST API.
Xray REST API provides the following endpoints.
Pre-Condition Tests
To view the Test associated with a Pre-Condition you need to specify the key of the Pre-Condition you wish you view. To associate or remove a Test from a Pre-Condition you need to send a json with a list of the Test keys. To remove a Test from a Pre-Condition you need to specify the key of the Test you wish to remove.