So I went down the rabbit hole of the meaning of "champ", thinking it might mean something esoteric in the context of "champing at the bit" like "speaking the first line of the skit". But no, "champ" as a verb is just an alternative version of "chomp", or at least a word that differs very subtly from "chomp".

https://www.merriam-webster.com/dictionary/champing%20at%20t...

https://www.merriam-webster.com/dictionary/champ

The migration of "champing at the bit" to "chomping at the bit" is inevitable.

There don't seem to be many idioms like this, where the newer version is both semantically intuitive/meaningful and accepted by authorities. The closest is probably "hone in on", but the verb form of "home" as in "homing device" is still current, unlike the verb form of "champ". Another interesting one is the migration from "just deserts", using an archaic meaning of "desert" as in something deserved, to the modern form "just desserts". However there's much greater distance between "desserts" and the archaic meaning of "deserts" than between "chomp" and "champ".