If you change the fluid and it starts slipping, putting the old fluid back in will not do any good. If the transmission is not slipping, do a service change. It will be a good thing. If by some strange anomaly it does start slipping, it isn’t because you changed the fluid, it’s because the tranny was already damaged. If you don’t have your tranny serviced it will fail sooner. If the tranny is slipping before you change fluid, changing it may help but not likely. The best recommendation I can give you is to properly service this transmission, and never reinstall old fluid. Or better yet have a professional that is familiar with the Honda protocol do it.