I'm not sure if understood the question, if you mean how to add a tint to a spot, here's how...following on your previous post example..
newSpotColor.spot = newSpot; newSpotColor.tint = 50;
No. That's not what I want.
To use your example. this newSpotColor is 50% tint of newSpot. Illustrator will calculate what the color looks like. But I want to tell Illustrator what this 50% tint color looks like. I have the exact Lab value of what the color should look like at 50% tint and want Illustrator to use this value for internal tint interpolation calculation. So that if a user selects a 50% tint in the UI he does get a color based on my previously inserted Lab value.
You can use a program such as Photoshop that understands LAB color space. Using the color picker, you can input those values into Illustrator as RGB values. Illustrator only uses RGB and CMYK. Also, you will need to know what color profile you need. See here:
Input your LAB values into the color picker and it will translate them to RGB for you.