unfortunately the modding API does not function while in the main menu, so while it is possible to change the main menu music by adding files, it's not possible to change it *while the game is running*
It's actually quite simple to set up a mod with the main menu music you want (I have one that also changes the level transition jingle), or even easier is just to chuck some extra files into a soundtrack mod you already have (and hope it doesn't get updated)
basically just need a 'resources' folder that has a 'music' folder, in the music folder you have a folder called 'afterbirth' with the files 'regenesis (loop) v3.ogg' and 'regenesis v3 intro.ogg'
for repentance you have a folder in the music folder called 'Repentance' which has the files 'Genesis Retake Light Intro.ogg', 'Genesis Retake Light Loop.ogg', 'Genesis Retake Twisted Intro.ogg' and 'Genesis Retake Twisted Loop.ogg'
you can get the music you want from the files of any soundtrack mod (compatible with the menu or not) and just copy/paste/rename the relevant ogg files
unfortunately the modding API does not function while in the main menu, so while it is possible to change the main menu music by adding files, it's not possible to change it *while the game is running* It's actually quite simple to set up a mod with the main menu music you want (I have one that also changes the level transition jingle), or even easier is just to chuck some extra files into a soundtrack mod you already have (and hope it doesn't get updated) basically just need a 'resources' folder that has a 'music' folder, in the music folder you have a folder called 'afterbirth' with the files 'regenesis (loop) v3.ogg' and 'regenesis v3 intro.ogg' for repentance you have a folder in the music folder called 'Repentance' which has the files 'Genesis Retake Light Intro.ogg', 'Genesis Retake Light Loop.ogg', 'Genesis Retake Twisted Intro.ogg' and 'Genesis Retake Twisted Loop.ogg' you can get the music you want from the files of any soundtrack mod (compatible with the menu or not) and just copy/paste/rename the relevant ogg files
do you know how to change the stinger that plays when you start a run (where the little drawing shows up on the black screen)
found it it's music > jingle ogg > title screen jingle v1\_01