That document says the same as I said above.
"if two doses of different mRNA COVID-19 vaccine products are inadvertently administered, no additional doses of either product are recommended at this time"
No nothing actually bad is expected to happen, it's just an unknown.
I’m not sure what you are trying to prove here. I was quite clear in my response. Also, from the same document it says they are not to be used interchangeably.
Yes, probably nothing bad will happen but you are missing the point. In medicine we don’t go along with maybe it will work when we have an alternative that we know it works. It has to be compared and validated. In this case it has to be shown that it is as good as the current vaccines, not that you will have no bad reactions.
The text mentions not to administer another dose if the second was INADVERTENTLY the other vaccine, because we don’t know what could happen yet and the first principle is “do no harm”.