Since I usually have multiple ACPs open during testing, is there an easy way to change the title of the ACP in the upper-left corner from IPS Community Suite to something else.?

Under 3.x, I changed the admin logo to something different per test site.

It's hard coded in the ACP global template. You can't get to it when you edit a theme from the ACP but you can if you enable designers mode. Or you can get Spacious ACP now available in the marketplace which changes the link that opens your site from the ACP that is just called "site" to your actual site name which would do the job as well. Not self promoting at all...

Thank you for your answer.

For now, I am using the Admin notes field.

I will look at Spacious ACP once I go live with 4.0.