Is it just me or the game couldn't care less about the settings in the ITUNs of the two SingSong interactions?
With game version 1.67 at least. My Sims are killing me - singing all the time - and lately I'm just doing very
short testing sessions.

0x03B33DDF-0x00000000-0x010008E4290C7561 SingSongInteraction_Sim
0x03B33DDF-0x00000000-0x36EEA342E0B13F86 SingSongRomanticInteraction_Sim

It's a Social Interaction. If you want to stop them from autonomously doing that, check >>> S3_0333406C_00000000_4A58252EEA3C6B09_SocialData_EP1%%+_XML.xml

Then find the Action Key "Sing Song" and "Sing Song Romantic" and set the <Available auto> field to false

EDIT : Or use this mod which apparently accomplishes it by modyfing the 2 ITUNs you mentioned and changing the Advertising values. That's another route, if you don't want to override the other resource.

That mod doesn't work (anymore). Setting negative advertising was the second
thing I tried. The third was making the interactions available only to Elder Horses...
that's why I said it seems the game doesn't care about the ITUNs.

The XML way on the other hand looked promising but doesn't work either. I'm puzzled.

EDIT: I guess I should have mentioned that my sims have the asian culture trait,
so maybe their singing is hard-coded. Damn it! I'm not absolutely sure if the
option in AwesomeMod is about this kind of singing, but that's not helping either.

Try these

S3_03B33DDF_00000000_4C9D91DE40D12F1D_PerformSing_Sim%%+ITUN.tuning
S3_03B33DDF_00000000_66A7A8C3FC23A019_TeachSongInteraction_Sim%%+ITUN.tuning

Also check in the SocialData_EP1 file, cos they're both Social Interactions too. These are the last two interactions used to sing songs, other than that there's no hardcoded reference to always let Asian Sims sing, at least in the SingingInfo class, which should be all there's to it.

EDIT : If that still doesn't work, you could try setting the <AutoLearnTrait> field to Unknown in >>> S3_0333406C_00000000_FB39FCD7FB3DCFB6_SingingSongs%%+_XML.xml

It was PerformSing ITUN. Didn't check that cause I was convinced it was related to Showtime.

So, to recap, all it takes is to set DisallowAutonomous to True in these 3 ITUNs:
0x03B33DDF-0x00000000-0x010008E4290C7561 SingSongInteraction_Sim
0x03B33DDF-0x00000000-0x36EEA342E0B13F86 SingSongRomanticInteraction_Sim
0x03B33DDF-0x00000000-0x4C9D91DE40D12F1D PerformSing_Sim
(they can teach songs to each other all day long as far I'm concerned), no XML editing is required fortunately.

I should have noticed that the serenade interaction had been actually disabled by the ITUN,
I guess I'm trying to do too much things at the same time.

Thanks for helping me, I appreciate that.

Glad I could help, you're welcome