When installing net-print/cups with both 1) USE="usb" and 2) CONFIG_USB_PRINTER=y in kernel you get an error advising to reconfigure the kernel. The easier alternative of disabling use flag "usb" for that package, say be running # sudo sh -c 'echo "net-print/cups -usb" >> /etc/portage/package.use/net-print--cups' is not mentioned. Please mention that alternative in error output. Thanks.
Done, thanks.