code: public void savePreviousImplementedVersion(Page page, Integer version) {
          String value = version != null ? String.valueOf(version) : null;
          ContentEntityObject entityObject = getContentEntityManager().getById(page.getId());
          getContentPropertyManager().setStringProperty(entityObject, PREVIOUS_IMPLEMENTED_VERSION, value);
      }
docs: Saves the sprecified version as the Previous implemented version
  
  @param page a {@link com.atlassian.confluence.pages.Page} object.
  @param version a {@link java.lang.Integer} object.