Was Voq the first Klingon to undergo choH'a, or was this process already an established ritual when Voq was ordered to undergo it? It seems reasonable they have used it for other races in other conflicts as well, such as becoming a Romulan.
From Memory-Alpha (emphasis mine):
The only confirmed application of the protocol was the transformation of Voq in 2256, for the purposes of infiltrating USS Discovery and learning its secrets. When asked if there were others, a House of Mo'Kai operative involved in the operation claimed that he was the test case. (DIS: "The Wolf Inside", "The War Without, The War Within")
source: Memory Alpha - choH'a'
In-universe, the process was apparently not used when Arne Darvin infiltrated Star Fleet as a Federation undersecretary's aide but was discovered with a simple body scan. (ST-TOS - The Trouble with Tribbles / ST-DS9 - Trials and Tribble-ations)