Not possible to cast different spells based on CD.
Code:
#showtooltip
/cast [stance:0][mod:alt]Rocket Jump;Demon Leap
Will cast Rocket Jump in human form or when ALT is held (to force it while in demon form. In demon form will cast Demon Leap.
Code:
#showtooltip
/castsequence [stance:2]reset=45 Demon Leap,Rocket Jump;Rocket Jump
This will cast Rocket Jump in human form. When in demon form it will cast Demon Leap then Rocket Jump, resetting after 45 seconds of the macro not being pressed (Demon Leap CD).