When does emerge read make.conf?

[D-LINC]

Recently I started a merge, but then while it was merging I wanted to edit my USE flags (for unrelated reasons) in make.conf. But I was afraid to do this, imagining that some how it might mess up the merge session. Once an Emerge session has started, are all the environment settings fixed for all the packages being built, or does make.conf get read multiple times throughout the builds?

[Genone]

make.conf (and package.* files) generally is only parsed during the initialization of portage. However there are a few cases where emerge reinitializes itself (like when portage itself is updated) which would cause make.conf to be reparsed.