I made new folder in script/nvidia same way as there is other versions, and downloaded nividia drivers there. Then I modified minimyth.conf.mk and check-file to allow this version to be build.
It built succesfully without errors. But when I try to run minimyth, it complains "can't load NVIDIA kernel module"
What went wrong?
However, one thing you did not mention was whether or not you modified the definition of NVIDIA_EXTRA_VERSION in script/nvidia/nvidia/package-api.mk so that at accounts for version 270 as well as 256 and 260. If not, that could cause a problem.
Anyway, I have added the package nvidia/nvidia-270.30 and committed it to SVN. It builds and runs on my Acer ApireRevo 3610.