Feature summary (what you would like to be able to do and where):
Special:InvestigateBlock should allow CUs to use different notices for IPs and accounts so that they can tag accounts with a notice that links to a case / another account while not doing the same for IPs.
Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
CUs currently if using the notice options cannot use a non-specific notice content when blocking IPs and accounts in the same form as it would link IPs to accounts. Furthermore a non-CU could look at the log / contribution page for a CU and see that these IPs and accounts had the same notices placed, which would strongly suggest they were blocked using the same Special:InvestigateBlock form and therefore are likely connected.
Benefits (why should this be implemented?):
It would allow CUs to use Special:InvestigateBlock for IPs and accounts at the same time without risking breaking disclosure agreements.