The reasons in the dropdown can be configured here : MediaWiki:Ipbreason-dropdown
The options for block duration can be configured here : MediaWiki:Ipboptions
However I can't find documentation on how to configure the default selections for the "Block details" section.
Specifically the option to block the IP from creating user accounts.
On my wiki (afwiki) this option is enabled by default, and I don't think most users see this. I am trying to prevent the situation where someone bans an IP indefinitely AND prevents the IP from creating an account.
P.S. I was not logged in when I posted this question. Not sure how to change it so that it pings my account (User:Rooiratel) instead of the IP.