Yes, you can modify any brush to have the opacity controlled by pen pressure using the controller editor.
First, open the editor (the power plug icon just bellow the menus), and select the opacity output.
Then around the top right of the editor you'll find a "Behavior scheme" label with three icons. Click on the first one to open the preset window.
Then choose the "Pressure func cubic" preset, click load and that's it, you have assigned the opacity to the pen pressure!
You can do that for any parameter you like, or even get blocks from the folders on the left and create your own parameter behavior. And that's actually how every brush in Black Ink was made!
The good thing about presets is that they include a few math tricks that make that pressure block a lot more comfortable to use without you ever worrying about it
And in the full version, when you have customized your perfect brush, you can save it and give it a name for future use.