This is what you said:
I know you can make mistakes unistalling iOS, but many people had problems downgrading iOS without disinstalling old one.
There is absolutely NO problem to downgrade a cIOS, you probably did something awfully wrong for that to happen.
So, as I never hear about bricking for unistalling and reistalling cIOS, I don't understand the real meaning of your first post
I never said anything about a brick for unistalling and reistalling cIOS. You're misunderstanding. Waninkoko's cIOS installs as IOS 249, which is currently not in use by the Wii, so you can mess around with it without problems. The brick comes if you do something wrong with regular IOS (note that there's no c there) (e.g. IOS 61, 70)
but as I said it's better to delete cIOS (rev. 14/15/16 **) and then install rev.13b. Again, it cannot damage anything in your system (even if you got a brick, which never happened as long as I know, you can still start wii via bootmii or preloader and fix everything), but some people have problems with superdump and a downgrading cIOS (for example I had problem the first time).
It's not better. It won't damage your Wii, but if for some reason someone that had cIOS (as IOS 249) and after that updated the Wii's regular IOS's and did not leave a vulnerable IOS besides the cIOS, that person would have to run TBR again if he/she uninstalled the cIOS. This isn't a brick, just a unnecessary annoyance, that could have been avoided if the person had just overwritten the cIOS with the previous version. This scenario might not happen to many people, but it is possible.
but many people had problems downgrading iOS without disinstalling old one.
What problems? Seriously. This was the first time I heard this. What cIOS did you have before you installed rev 13b.
I've done this procedure tons of times with all revisions of Waninkoko's cIOS's without a single problem.
If you're talking about the 99% issue with Superdump, this has got nothing to do with installing an older version over a newer one. This happens with all versions of cIOS. You can ask kiczek about it.