Did you actually tried this? Because, when i tried this at the beginning of the game, you couldn't change Guard place after you equip the Shield... It's for that reason that I never equip an ability on X slot for let a space for Guard to auto-equip when I equip my Shield.
Yea, you can't move guard doing that. What I do is this.
At the beginning of the macro use: /eaction 4 ""
This clears the skill out of slot 4 (where I want my Guard, this is an example, change it as you like).
Then you start filling your bar with Light slash, Light Stab, Heavy Stab, then at the 4th slot, equip your shield, and Guard will automatically be set to that 4th slot that you opened up at the beginning (guard is always set to the first open slot on the bar.
Not using the slot for guard seems a little overboard, I hope this tip helps. I really wish they would make it so each class stores all of the skills on the bar. Using macros to do this is just stupid, slow, confusing at times, and time consuming. I have 2-3 macros for each class, one for every craft class, and 1 for every harvesting that I have to constantly update. As well as gear swapping macros. This really needs to be simplified and sped up. Edited, Nov 24th 2010 2:21pm by MattVid6