Hi,
I am not sure you have a complete understanding of the App in it's current form.
The Messages app can have an iMessages account and up to 4 different IM account (Instant Message) such as AIM/AOL, Jabber Yahoo or the Bonjour account.
The iMessages account deals with Contacts and works from the Contacts app to link to people.
The other have Buddy Lists (Separate windows within Messages that can be displayed from the Window Menu)
If you have no Buddy list Account active and therefore not Buddy List window on show then the Buddies Menu will be mostly greyed out
As you can see the Messages main window/Chat window/Interface is the active one.
I have several Buddy Lists on show but the Buddies Menu cannot Add a Buddy.
It will change if the Chat is to a Buddy rather than a Contact (i.e not an iMessages conversation) or if the Buddy list is "Front"
Normally the first thing the Mac version of Messages does is ask you for an Apple ID to register with iMessages.
this is because the iMessages and Bonjour accounts are there by default.
The iMessages one needs an Apple ID and the Bonjour one finds other Macs on your LAN and uses the Contacts app as your "Buddy Name" if you Enable it (it is Not Enabled by default).
Therefore you are Logged in if the iMessages account is Enabled.
The Status item only applies to Buddy Lists so you can not use this to become "Available" in the iMessages account.
The only way you know it works is when you select a Contact and send them an iMessage.
Let me say this another way:-
Originally there was iChat.
It had Buddy List and you clicked on the icon at the bottom of the Buddy list after highlighting a Buddy or double clicked the Buddy and the Chat window would then open.
Over the years Video and Audio Chats have been added then Jabber and later Yahoo.
The iMessages account was added when it became Messages and the main Messages Interface/Chat window became the main item.
Buddy Lists are no longer displayed by default.
The iMessages account accesses the Contacts app by either typing directly in th "To" Space or using the Blue + icon on the right after starting a New Message.
Most of the Menu items apply to the iChat functions such as the one where you can change the Status Messages for an Account and the type of Status it is.
The iMessages account just logs in (blindly if you like) when it is Enabled
The only time you know there is a problem is if it gives you an Error Message on Registration or when Enabling the account or if it cannot Send iMessages to Contacts.
To restate many Menu item might appear greyed out as they refer and work with Buddy Lists and not the iMessages account.
There in nothing to tell you the iMessages account has Logged in.
You cannot change it Status from the menu item.
Up to Mavericks/Messages 8 you can't permanently change the Buddy Pic until you have a Buddy list Account active. (Just enabling the Bonjour Account abut keeping the Buddy List hidden even if you have no other Macs on your LAN is enough for this).
9:29 pm Monday; October 27, 2014
iMac 2.5Ghz i5 2011 (Mavericks 10.9)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad