src.conf(5) to specify multiple flavours of a port

In a thread elsewhere, as an example that did /not/ involve src.conf, 
Mark Johnston wrote:

> $ cd /usr/ports/graphics/gpu-firmware-intel-kmod
> $ sudo make reinstall FLAVOR=kabylake

How might I use /etc/src.conf to achieve much the same, with a different 
port?

A recent edition of my file included these four lines, the third of 
which causes an error:

PORTS_MODULES= graphics/drm-510-kmod
# PORTS_MODULES= graphics/drm-515-kmod
PORTS_MODULES+= graphics/gpu-firmware-radeon-kmod@btc 
graphics/gpu-firmware-radeon-kmod@sumo 
graphics/gpu-firmware-radeon-kmod@turks
# PORTS_MODULES+= graphics/gpu-firmware-radeon-kmod

This morning: I use the fourth line, instead.

In future: I'd prefer to be without the build time that's associated 
with so many flavours, when only three are required.

<https://www.freshports.org/graphics/gpu-firmware-radeon-kmod/#flavors>


More than doubly time-consuming, because:

KERNCONF=GENERIC GENERIC-NODEBUG
# KERNCONF=GENERIC
# KERNCONF=GENERIC-NODEBUG

NO_INSTALLEXTRAKERNELS=no

TIA