Yes, you can rename an existing criterion at any time from ReviewX → Reviews → Review Settings → Criteria — existing ratings and graph data for that criterion stay intact and continue displaying.

The one thing worth being careful about: keep the meaning close to the original when renaming (e.g. “Color” to “Product Color” is fine, “Color” to “Shipping Speed” isn’t) — otherwise past ratings on that criterion no longer reflect what the new label claims to measure, which is confusing for shoppers reading the breakdown.