Yep, currently brave (and others I assume) switch it on at build time, when Google removes that from chromium they may move it to their patch set, but who knows how long they’ll keep that once it starts breaking.
But Google haven't made those changes to how web requests are performed yet, so it's impossible to say how difficult it will be to add back whatever functionality is necessary to add back dynamic web request hooks. Maybe it'll turn out to be relatively easy, and maybe Google will leave that part of Chromium relatively unchanged for a long time. Only time will tell.