Contagiousness can certainly increase. Virulency does not usually increase.
Severe flu seasons are characterized by increased infections, not so much increased fatality rate.
> Citation needed.
"Most viruses become less deadly as they mutate." https://www.economist.com/the-economist-explains/2021/02/27/... (The article is about how COVID might buck the general trend. But in any case, that is the trend.)
My point is that we simply do not know. The word 'usual' is deceptive here. Usual for the viruses we studied? Usual for all viruses? Usual for viruses which recently have made the jump to a new species? We do not know. We simply have no idea.
> no idea
This type of reasoning is based on an assumption that a pathogen limits its reproductive number by increasing its virulence. It is reasonable to test this hypothesis, but unfortunately we do not have enough data points to make any conclusive statements.