Sorry for the late response, I read your posts, but haven't had time to test it until now!
Those are good ideas! I tested the latter one.
Technically it works, the sounds play when unpatching during the MakeVoice method, but it only works when I removed the patch from the Initialize method (which is called from "MBSubModuleBase.OnSubModuleLoad"!).
This had me worried, because it would require the player to issue a command or otherwise trigger a voice callout first to have the patch apply at all.
In other words, if I patched it via "OnSubModuleLoad" at all, the callout would fail to play!
Which got me thinking that the issue is not related to the patch being applied during the moment the callout is supposed to be played, but rather, it is related to when the patch is first applied.
Subsequently, I tried applying the patch at a later point, first going with "OnGameStart" (and unpatching on "OnGameEnd", just in case). This worked, with callouts playing despite the patch being applied.
I settled on applying the patch via "MBSubModuleBase.OnInitialState". This method seems to be called after the game has loaded into the main menu, and applying the patch here fixes the issue, without having to unpatch/patch at some point, interestingly enough.
Thank you for your solutions, definitely helped give me new ideas for how to approach the issue!