reformo

Is it re- plus formo? Honestly: nearly. Both parts are real Esperanto. Re- is the productive prefix for doing a thing again, and formo is a shape or form. So reformi looks like it should mean to shape again, and historically that is precisely what the Latin meant. But PIV treats reform- as its own root, and it is right to, because the modern meaning has narrowed: a reformo is a deliberate improvement to an institution, a law or a system, not any old re-shaping.

What that means in practice. If you build the word from the prefix instead, writing it as re-formi, an Esperantist will read it as to form again: re-moulding clay, re-setting a broken bone, re-shaping a paragraph. The fused root reformi is what you want for reforming a school system. In speech the two are indistinguishable, so careful writers reach for refari or rekonstrui when they mean the literal thing.

The word carries a scar in this language. Reform is not a neutral term in Esperanto history. Proposals to reform the language itself have followed it since 1894, when Zamenhof put his own set of changes to a vote and lost, and they culminated in the Ido schism of 1907, which cost the movement a slice of its leadership. The settlement that came out of it is why the Fundamento and the Academy work the way they do: the language grows by addition, not by reformo.

Around it. Ŝanĝi is to change, plibonigi is to improve (literally to make more good), reformisto is a reformer, and reformema describes someone inclined to reform things whether or not they need it.