Is packet injection easily detected?

[Zezombye]

I want to make a custom game bot for more advanced gamemodes like BR, Infection, etc.

AFAIK the only thing that exists is Deltin's bot (http://www.abyxa.net/Library/Library.html), but it functions by pixel-testing. From what I've seen aimbots that do that are detected very easily and your game is screenlocked, so I don't know how the bots aren't banned yet.

Anyway, as this bot requires an alt account (which I don't have) I'd like to create a bot which reads and injects packets, so that I can play while changing settings, swapping players, etc. For that I'd just need to know what packets are sent and just replicate them (though I still have to decrypt the WOW protocol).

Is this packet injection easily detected; will bliz ban me automatically, or will they turn a blind eye as it's only for custom games? (as I assume they do with pixel-reading bots)
Also, if I get banned, is it for life, or like a few days for the 1st offense?