Yes. You can register as many different passkeys as you want. Any limitation in passkeys registration quantity is a limitation of the website/app itself and not a limit of the spec, etc.
If the developer fucks up the website/app, that is their fault and not a failure of the technology.
Respectfully, you should consider reconsidering this mindset. The best engineers and tech designs take into account not only how users will use a technology but also how they will misuse it.