EDIT: Ignore the stuff below and read Adam’s answer:
I don’t know enough about how everything works to understand the implications of doing that. You could try ejecting and then reverting the Android-specific changes, but it might cause problems.
One thing that comes to mind is that you could have a branch where you eject and a branch where you don’t.
Then you could develop the Android app on the ejected branch and the iOS app on the managed branch. This is far from ideal, though, because you would have to basically copy common changes between branches all the time.
Maybe look into monorepos. I have not tried them before so again I’m unsure of how everything works, but maybe you could essentially have two separate projects for the Android and iOS versions of the app, but you could move the bulk of the code (everything that’s shared) to basically a library that you use from both of the apps.