Tank vs DPS class doesn't matter. I use the same priority system for my tank, healer and DPS.

You have a couple of options -

1. Lacerate has a 3 sec cooldown and only stacks 3 times. Mangle has a 6 second cooldown. You can work out a castsequence to get lacerate up and then prevent it from recasting after that for 15s or so as your top priority

Code:
/castsequence reset=target Lacerate, Mangle, Lacerate, Lacerate, Mangle, Mangle, Mangle
then replace that bottom priority Lacerate with another Mangle key to soak up proc'd Mangles {this way Mangle procs get used to advance the castsequence above anything else}

2. Use something else to temporarily lock up your Lacerates

Code:
/castsequence reset=target Lacerate, Lacerate, Lacerate, Growl, Growl, Growl
3. If Lacerate refreshes the 15s bleed, then it's going to end up being a waste of GCDs to let it drop and them put all 3 up again. In that case, I'd probably consider doing a nulled castsequence of 3 Lacerates and then adding Lacerate to something else, like

Code:
/castsequence Thrash, Thrash, Lacerate

For the hunter, it looks like generated focus should default to Chimera and only be used for Arcane when you need a focus dump. That being the case, I'd opt for random casts or Steps in conjunction with the priority system.

My Paladin Tank is a good example of this with Word of Glory. I glyphed her to use WoG as a damaging spell as well as a heal, but even unglyphed, you don't want to spend all your Holy Power spamming the crap out of WoG when you really want it for Shield of the Righteous. So, it's all well and good to put WoG on the bottom of the list, but it was still casting too often and eating the Holy Power I wanted for SotR, since WoG can cast with as little as 1 Holy Power, while SotR will only cast with 3.

So instead of just sticking my WoG button on the end of the priority, I added a key that calls a set of toggles/steps

Code:
//* TANK TOGGLES
<Hotkey RAlt F9>
	<SendLabel w1>
		<Key Shift 1>
		<Key Shift 2>
		<Key Shift 3>
		<Key 2>
		<Key Shift 4>
		<DoRandomToggle Hotkey Oemax 2>
Then I made those toggles/steps refer to "blank" keys 4 times and my WoG key only once.

Code:
//* WORD OF GLORY
			
<Hotkey Oemax 2>
   <Toggle>
	<SendLabel w1>
	<Key Shift 5>
   <Toggle>
	<SendLabel w1>
	<Key Oem4>
   <Toggle>
	<SendLabel w1>
	<Key Oem4>
   <Toggle>
	<SendLabel w1>
	<Key Oem4>

Because HotkeyNet can't have true "blank" toggles, I uses Oem4, which is a keybind on a blank key in game.

This further reduces my chance of spamming WoG every time I get Holy Power because there's only a 1 in 5 chance that HotKeyNet is going to trigger Shift 5.

Don't know details on how you can manage the same thing with ISBoxer, but I'm sure you can use the whole Do Not Advance thingy on your Arcane Shot or add Arcane to a /castrandom macro at the bottom of your priority that calls Find Herbs or some other non-GCD-inducing/no cost/no cooldown ability a couple times or something.

Or you can tie Arcane to something else like I pointed out with the bear macros. A priority system does not exclude the use of castsequences or steps. From what I've been seeing it's best used in conjunction with them.

Really when it comes down to it, there's dozens of ways to make things work, it's just a matter of thinking creatively and experimenting.