At the repository level, package.mask has been supported for some time.
Support for use.force, package.use.force, use.mask and package.use.mask
was recently added in commit
96ab7b436ceb3543f5158aab1fab48470c3f0b98.
info_vars
license_groups
package.mask
+package.unmask
+package.use.force
+package.use.mask
profiles.desc
repo_name
thirdpartymirrors
use.desc
+use.force
use.local.desc
+use.mask
.fi
.TP
.BR /usr/share/portage/config/