I'm not sure having two spells in a macro using /cast that trigger a GCD will work the way you want it.

I believe all a macro with /cast Shadowbolt as the first line will do if you use it while moving is throw errors at you about how you can't cast that while moving.

I think the general rule is that the first /cast that triggers the GCD is executed and the macro is considered "done" regardless of whether the /cast was successful.