If you use custom state definitions (the "Custom" checkbox) adding the possess state will change the order of pages, and since buttons are linked only to the page number, not the page state, you'll now have an extra page and bump all of the rest of your pages down the line, and your buttons will all be on the "previous" page from where they were before. But if you set up paging using the checkboxes, this doesn't apply to you at all and you can just follow the directions in the FAQ.
Read the FAQ linked on Macaroon's download page, specifically under the section about creating a vehicle/possession bar. It's extremely simple to add a vehicle/possess "page" to an existing bar, though you will probably have to reconfigure the actions on the bar, since adding a new state will alter the page ordering.
If you weren't using custom states, then the possession bar issue you describe is a bug... if you are using custom states, you probably have an alt page defined that supersedes the bonusbar:5 page. Order of declaration is important!
For macros like IHML etc, you could just bind a key directly to the macro using Macaroon Binder (found in the optional Extras package) rather than deal with the hassle of swapping them back and forth.
I'm not sure why you're seeing your buttons switch to actionID buttons; where are you dragging and dropping your abilities from? The only time I've ever seen them switch to actionID buttons is when they're supposed to -- when you drop on a macro that was created in the Blizzard macro UI, or when you drop on a mount or minipet. Could you give me a specific example of something that turns a button from a macro button into an actionID button? Which ability did you drop onto the button, and where did you drag it from?
As for your other requests, Macaroon can show you the duration of buffs on yourself and debuffs on your target. Enable "text buff/debuff timers" in the Interface Options menu panel. The addon Seerah linked should be able to do the rest.
Also, if you give your Macaroon macros names, they will show up in the "saved buttons" panel, and you don't have to recreate them if you want to swap them out later.
"/mac edit" or alt-click the minimap icon to enter Button Edit mode. Each button will have text overlaid on it saying either "action id:N", "pet id:N", or "macro".
By default, every button is a "macro" button. I'm not entirely sure what the rules are governing when the addon will change a button to "action id" on its own, other than that dragging a macro or a minipet/mount onto a button will always change it to "action id". If you're using a macro, I'd suggest not dragging and dropping it on a button, but rather copying the text out of the macro and inserting it directly into the button by entering Button Edit mode, right-clicking a "macro" button, and pasting the text into the box that pops up.
Also, I'm going to split these Macaroon posts off into a separate thread, lest poor JJ come back and find his thread filled with stuff not even related to his addon. :p
If it's messing with buttons on the Blizz bars, then you've got your Macaroon buttons set to use actionIDs instead of the default macrotext type. Enter button config mode and left-click each button until it reads "macro" instead of "action id".
As for trinkets, what are you wanting to happen, and what are you currently doing to try to make it happen?
No it doesn't... don't turn off the Blizzard bars in its menu. They are not disabled by default, so if they are hidden, either you turned them off, or you have another addon hiding them. Macaroon bindings will override the Blizz bar bindings, so if you want to use the Blizz bars, don't give a Macaroon button the same binding as a Blizz button.
Can you guys maybe suggest me any other bar mod that is capable of displaying dogtags the way Infinibar can (could)?
That was the main feature I preferred Infinibar to Trinity (which I was using before, and as it seems Macaroon is the followup to Trinity)
DogTag is an evil bloated monster. When I ran InfiniBar, it was the only thing using DogTag, and only for keybind text and action count text. With over 200 addons running, DogTag used almost as much CPU time as every other addon combined... and that's not counting the significant CPU usage of the Rock framework, which was also used only by InfiniBar. When 3.0 hit and I switched to Macaroon, ditching DogTag and Rock in the process, I gained about 10 FPS in raid combat situations, and significantly more while idling.
What did you use the DogTag display for? Depending on your answer to that, there may be a non-DogTag alternative already working that doesn't depend on any specific actionbar addon.
I second that, or otherwise can somebody suggest a bar mod that is capable of addressing different ctrl / alt / shift state pages in EACH stance? Macaroon behaves much like Trinity used to in the sense that you get to the same page with, say ctrl held down regardless of your stance. Also something not restricted to the standard 120 blizz action slots would be nice... if such still exists after 3.x :)
Macaroon is perfectly capable of doing what you describe, and is not restricted to using the Blizzard action IDs. Enable custom states and define something like: