That is the entire point of the macro - to get in as many firebolts as possible/circumvent latency issues, while at the same time not accidentally telling your pet to attack things it shouldn't be attacking. You still have to initially tell it to attack a target, and switch its target when you switch.

This is another variation, posted in the destruction thread (yay search function):

#showtooltip SPELLNAME
/petattack [target=pettarget,noexists] target
/cast [@pettarget, exists] Firebolt
/cast SPELLNAME

Here is what I do in order to control what is imp attacking. I use /petattack in same macro with Bane of Doom. This way you are only telling imp to attack targets with a lot of health so burning embers can stack up properly and imp will not attack low health adds as you are not casting bane of doom on those, normally.

As you cast bane of doom every 1min or at start of fight it will minimally pause imp attacks, as /petattack line does that, and it is natural to connect these two things, bane of doom and burning embers as they function similarly.

From a min/max perspective, through Simcraft, I'm finding that Glyph of Bane of Agony is a slight DPS increase over Glyph of Corruption. It's not a significantly large difference, ~30-50 DPS.

Are any other affliction seeing this as a repeatable result? Is there an advantage to keep Glyph of Corruption at this point from a DPS perspective?

Has there been any testing done with the glyph of BoA and how it scales with haste? I'm assuming when you get additional DoT ticks this might be helpful to know how the glyph affects those extra ticks gained through haste.

If doing drain affliction ive found nightfall and Corruption glyph gives me enough instant shadowbolts to keep the 5% shadow & flame up. Also you get more out of corruption glyph on trash as they are down before the extra time of BoA kicks in

Saufsoldat, this macro should do what you want it to, though whether it will give you maximum pet dps is a slightly different matter. This macro will cause your pet to change target automatically when you do, when you cast the spell you attach it to- I'm going to use Immolate in this example:

#showtooltip Immolate
/use Immolate
/petattack [@playertarget] Firebolt

You can add in [harm,nodead] modifiers according to personal preference. The macro works best with the Imp on passive (great if you're opening with a glyphed Fear pull) as the syntax needs to change slightly for pets left on defensive. I think that it would be a dps loss to add that line to Incinerate as we tend to spam that, which may interrupt any new Firebolts the imp had begun casting whilst we were finishing our previous Incinerate cast, but I can't get in game right now to test. I cannot attest as to whether this will allow your imp to cast the maximum number of Firebolts under every possible circumstance, but it does save you hitting Ctrl+1 and saves Firebolts being 'wasted' at a lower priority target.

You might get better luck with
#showtooltip SPELLNAME
/cast SPELLNAME
/cast [@playertarget,harm,nodead] Firebolt|Lash of Pain|Legion Strike

But I've moved away from @playertarget to forcing a target on him by putting on passive targeting, activating pet attack and leaving him on that while I feel free to tab target or CC or what-have-you.

Power Auras or some similar buff-monitoring addon.

When using the Affli Drain spec, after using demon soul should one spam shadow bolt for 20s as a filler or should one use shadow bolt once and come back to drain life as a filler?

You should respect the priority, ans as such, thus, use drain life until you have another insta-shadowbolt.

I haven't done extensive enough testing to be 100% sure, but I believe so. The 4.0.3 version of DS: Imp affected the damage of immolate's periodic crits.