How do I specify a custom dir for 'zcash-params'?

I hate to sacrifice ~1GB from my home SSD.

There is no option to do this. Perhaps you could create a symlink to map the expected directory to the custom dir?

That’s may be a workaround, but why not to provide this option??

There are a few tickets that reference this, so it is understood and I guess simply isn’t a priority with everything else going on: https://github.com/zcash/zcash/issues?q=is%3Aissue+is%3Aopen+params+label%3A"zkSNARK+Parameter+Deployment"