This is long, but please read it before downloading.
The game has some spots to add skills that appear to be unused. In my experiments, they've been set to zero. Maybe the game is using them in some undocumented way. I don't think it is, but it's important that people understand this before they choose to use this mod. This isn't the first mod of this type. There are a few from Chris Hatch that add different skills/motives, and I checked in with him a long time ago to see which spots he was using, so that I could use different ones.
The goal of this mod is to make music and art skills separate, so Sims can be talented musicians without automatically being a great artist. I have UC, and this mod is built for people using all the EPs. This overwrites semiglobals that affect every instrument in the game and the easel. It also adds a new global. Consider it incompatible with things like Argon's instrument hack and other painting/instrument hacks. If the mod ends up getting a full release, I'll edit in compatibilities. The DJ booth and skilling toys are not included in this mod right now (the activity table/xylophone).
This should only work for Sims who are currently selected.
How it works
Buy this painting for $0 in the Hobbies/Creativity section. Choose values for the art and music skills (or leave them at zero). Both the art and music skills need to be less than or equal to the creativity skill. But the values added together don't have to be add up to the overall creativity. You can have 3 points in art, two music points and seven overall creativity points, since you can raise creativity in other ways, like novel writing.
Set the art/music skills to a value between 1-1000, if you choose. If you don't set the art/music skill at all, the value will be 0. The skill panel shows a scale of 1-10, but in the code, one creativity point is actually a value of 100.
While this is in testing, Sims who are being affected by this mod will glow. That's visual confirmation that the controller the mod uses was created, and once the interaction is over, the glow will fade. The mod will set the Sim's creativity level to the art/music skill level until the interaction ends, then it will do the math to give the Sim the appropriate number of points. If Julian has one music point, and three overall creativity points, then he gains one skill point playing the piano, when the interaction ends, he'll have two music points and four overall creativity points.
To test - set up a back up copy of your neighborhood, without any mods that affect the easel or music. Make sure no one is playing an instrument or painting before putting the mod in, then let Sims build the skills as usual. Use the painting to check the skill points gained in creativity and whatever skill you just built to make sure the math looks right. If you make the decision to use the mod in your main game, and you later remove it, you may want to go back and set the art/music values to zero.
Known issues - While a Sim is building creativity on an art/music object, they might roll a want to gain a number of skills they have already. With testing cheats on, you can hold control, then click the want to fill it. Example: A sim with eight creativity skills and 0 music skills might roll a want to hit creativity level 1, because as far as the game is concerned at that moment, they have no creativity points.
When using the microphone, the creativity skills gained is usually slightly more than the music skills gained.
I'm posting here to do my best to limit this to people who actually want to test mods. Please do not take it upon yourself to advertise it on higher traffic places like tumblr while it's in testing.