Change content type via reflection

change-content-type.cs

public class ChangeContentTypeController : UmbracoAuthorizedApiController
{
  private readonly IContentTypeService _contentTypeService;
  private readonly IContentService _contentService;
  
  public ChangeContentTypeController(IContentTypeService contentTypeService, IContentService contentService) {
    _contentTypeService = contentTypeService;
    _contentService = contentService;
  }

  [HttpGet]
  public IHttpActionResult Convert(int nodeId, string newTypeAlias)
  {
    var newType = _contentTypeService.GetAll().FirstOrDefault(x => x.Alias == newTypeAlias);
    if (newType == null)
        return BadRequest("Could not find content type");

    var originalContent = _contentService.GetById(nodeId);

    if (originalContent.ContentType.Alias == newTypeAlias)
    {
        return BadRequest("node has already been converted");
    }

    Type thisType = originalContent.GetType();

    MethodInfo changeContentType = thisType
        .GetMethod("ChangeContentType",
            types: new[] { typeof(IContentType) },
            modifiers: null,
            binder: null,
            bindingAttr: BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Public);

    changeContentType.Invoke(originalContent, new[] { newType });

    originalContent.TemplateId = newType.DefaultTemplate.Id;

    _contentService.Save(originalContent);

    return Ok();
  }
}