SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.
It already is disabled for other backends, but this didn't happen with the software renderer. Attempting to change it while running causes the change to visually happen (including switching to the normal render settings UI instead of the barren one for the software renderer), but doesn't actually change the backend itself (it'll still use the software renderer at the next launch).
Pierre Bourdon