You could also use the Litetween behavior
on function "fade in"
sprite set target value "opacity" 100
sprite start litetween
it will animate till it reaches 100 based on its property settings (eg: lerp, duration etc)
litetween allows you to specify a "value" as well that be used for anything that needs to change over time.
So you can say something like , set sprite.width to Sprite.LiteTween.Value to use in in circumstances beyond just the litetween basic properties as well