I always get aggro trying to reuse a regex that works on `rg` in `sed`. You

  rg "something I need to (change|modify)" file.md
  

  sed -i 's/something I need to (change|break)/$1 is inevitable/g' file.md

Ah yes! Extended regex...

  sed -e -i 's/something I need to (change|break)/$1 is inevitable/g' file.md

  sed -h 2>&1 | grep 'regex'
  -E, -r, --regexp-extended

But fastmod, which is mentioned in at the end of https://github.com/BurntSushi/ripgrep/blob/master/FAQ.md#search-and-replace is surprisingly good, both in terms of performance/ux and compatibility.

You just:

  fastmod -m 'something I need to (change|break)' '$1 is inevitable' file.md