Hi Roman,
Nice shop and nice little business! Thanks for sharing the pictures. I like the mod you did on the Jardine mounting, but I would keep an eye on the front mount and the muffler to collector joint for a while, just in case you get movement at that new rear mount which leverages on the front of the pipe. The only reason I think this is because of the single bolt, screwed into Aluminium, which holds the top of your bracket. The single bolt is a pivot point which could allow movement. It is difficult to get enough torque on fasteners in Aluminium to prevent pivoting on a single point. Not saying it will, it probably won't but I'd keep an eye on it.
The experts on this forum usually recommend NGK dcpr9eix spark plugs for our XBs, maybe the ones you put in are an equivalent, I didn't check.
You're right, opening up the intake will require re-mapping or a race ecm from Erik Buell racing.
To re-map and tune you need a cable, which you can buy from xopti (which is cheap) and a program called ecmspy (the older version which is all you need is freely available). You should probably get the cable and ecmspy in any case as it will allow you to reset and adjust your throttle position sensor, which will also help the bike run better.
You can buy an ecm from Buell which is set up for the combination of a Jardine and free-flowing intake, though it may not be perfectly optimized for your bike it will do a very good job.
You can also take courses online from The Tuniversity, which is the best way to go as then you can re-tune your bike anyway you want to at anytime.
Don't waste your money on a fuel card like a poweriser, I hear they don't last very well and can cause problems, your best bet it to re-tune your stock ecm or buy one from Erik Buell.
The problem with running too lean is that not only will you burn out your plugs faster, but you can also burn your valves and even put a hole in a piston due to inaudible pre-ignition. You will probably find the bike doesn't run or idle nearly as well either. It depends on how long you ride it and how hard before re-tuning or installing the race ecm. You put a lot of miles on yours and if you don't ride hard (heavy acceleration and deceleration, wide open throttle), it will probably be OK longer in cold weather than it would riding in 35C weather. You could probably ride for a couple of weeks, maybe a month with no significant damage, just some accelerated wear. Spark plug life will be shortened, but by how mauch really depends on information and varianbles I know nothing about, like what the AFV will be after the mod, how you ride, quality and octane of gas you run etc…
That is just my opinion and I'm not an expert on these motors. There are some folks on this forum that have way more experience with these engines and mods than I have and hopefully they'll comment.