You could create a reverse patch.
Get the standalone voice patch:https://forum.starmen.net/forum/Community/PKHack/MOTHER-3-Canonical-voice-patch
Then, get a 1.2 version of the Mother 3 English translation patch as well.
(Don't forget Lunar IPS or whichever tool patches the ROMs)
1) Patch a Mother 3 ROM with the 1.2 patch
2) Create a copy of that patched ROM, so you have 2 ROMs with the same English patch.
3) Patched the copied ROM with the Voice patch. Now you should have one ROM with the voice patch, and without. Be sure to name them to be able to differentiate them both.
4) Now here comes the interesting bit.
You will create a new patch. You need to create a patch that uses as the base ROM the ROM WITH the Voice patch, and the modified one will be the one WITHOUT the Voice patch.
Create that patch, and you now have a patch to have the old voice used in 1.2.
5) Apply that newly created patch over 1.3, and it should work (not guaranteed tho)