Right now, this does now work:
#showtooltip
/use [mod]Displacement;Shimmer
When I cast Shimmer and then hover the mouse to see the spell id in the macro (with idTip addon), it selects another Displacement spell (different spell id), so it says Spell not learned if I try to use it with [mod].
Today I tried the following below and it seems to fix the Displacement macro bug, at least the functionality works:
#showtooltip [nomod]Shimmer;Displacement
/use [nomod]Shimmer
/click [mod]MultiBarRightButton2
You just need to put the Displacement spell from the spell book directly to MultiBarRightButton2, which is the second place of the right vertical bar. You can change the place in the bars you want, I just selected MultiBarRightButton2 for testing this. Hope it continues to work, I refused to play mage these years because I refused to have 2 buttons for that, yes literally for that only.