Is there a way to add a user macro to the quick access toolbar (QAT) or the quick commands (the one that pops up when you hit spacebar in the graphics window)?
Yes it is possible. If you want to import an external macro to STAAD, you can do the same using the Utilities > Macro option. Also you can add the macro in User Tools which will help you to select the macro very easily from the dropdown list. Though User Tools cannot be included in the quick commands or quick access toolbar, still you can include the Macro option. Just include your code in Macro and when you launch it from quick command or from quick access, you can select the code easily. Check following figure --