Adding Main Commands with /chotbar /hotbar

[Rongway]

They can be set from the Actions & Traits menu as Mikey says.

Also, in the event you want to include them in a macro for some reason, all the Main Commands have dedicated slash commands which are literally just a slash followed by the thing you want.

• /battlestance, /bstance
• /actionlist, /alist
• /adventurerplate, /myplate
• /portrait
• /currency
• /character, /gear
• /armourychest, /armoury
• /inventory, /bag
• /saddlebag
• /companion
• /mountguide
• /minionguide
• /fashionguide
• /bluespellbook
• /pvpprofile, /pvpp
• /goldsaucer, /saucer
• /achievements

The long forms each of these are all in the autotranslator, so if you forget you can just type a slash, part of what you're looking for, and then tab to autocomplete it from the autotranslator.
e.g.:

• /arm[tab] => (/armourychest)

For more information on how to use each command, you can use the help command /? which will accept the commands with or without slashes, plain or autotranslated.
e.g.:

• /? bstance
• /? /pvpp
• /? (/goldsaucer)

I'm uncertain the purpose for which you would want to reassign main commands on the fly with a command, but if it's something you mean to do repeatedly, toggling the share state of a bar or limiting which bars are visible in and out of combat are probably the intended ways to do whatever you're trying to do...so...what exactly is it that you're trying to do?