A root in The Etymologies of the 1930s with derivatives having to do with quickness, suddenness and fierceness (Ety/BERÉK), replacing rejected ᴹ√MEREK and ᴹ√BHERÉK (Ety/MERÉK; EtyAC/MERÉK). One notable derivative is the name N. Bregolas “Fierceness”, which continued to appear as S. Bregolas (albeit untranslated) in later versions of The Silmarillion (S/148). It seems likely this root was also an element in the name Bregalad “Quickbeam”, first introduced in Lord of the Rings drafts from the 1940s (TI/419) and retaining this form and meaning thereafter (LotR/482).
One of the 1930s derivatives of this root was N. Dagor Vregedúr “Battle of Sudden Fire [bregedur]”, which in the published Silmarillion became S. Dagor Bragollach “Battle of Sudden Flame” (S/151). This hints at a possible revision of this root, perhaps to ✱√BARAK, though whether it was a transient or lasting change is unclear.
Neo-Eldarin: For purposes of Neo-Eldarin writing, I think it’s best to stick with ᴹ√BEREK and the forms from The Etymologies.
A root in The Etymologies of the 1930s glossed “valiant”, its most notable derivative is the name S. Beren “Bold”. It had a variety of derivatives having to do with daring, such as ᴹQ. verya-/N. bertha- “to dare” and ᴹQ. verya/N. beren “bold”. The continued appearance of the name Beren in the later versions of The Silmarillion implies the root remained valid, but this name was only translated in The Etymologies of the 1930s, so it could have shifted in meaning.