Hey. macros using different hotbar slots and buttons will work regardless of whether they're displayed or not.
For the actual syntax of a macro activating hotbar slots, the first number is the button number, and the second is the hotbar number. So for a macro using the first 3 buttons of the 4th hotbar would look like this:
/macro name /use 1, 4; /use 2, 4; /use 3, 4
Also, if you're trying to use abilities that require a casting time, it it important to put a pause command inbetween activating the abilities that corresponds with the casting time. For a pause, 1 second = 10. So for a 2 second pause in between each cast, the macro would look like this:
/macro name /use 1, 4; /pause 20; /use 2, 4; /pause 20; /use 3, 4
In addition to using macros like this for abilities, you can also use them to change clothes quickly by just loading the clothing into the hotbar same as you would anything else. I usually use Hotbar slots 11-20 for this.
Hope this helped