People love to modify their EUCs in all sorts of ways, ranging from altering the aesthetics, to changing their functionality. I’ll try and give my own take on each of the modification methods.
Covers and cases are awesome. I used a cover on my Kingsong 18XL and when it came time to sell it, it didn’t have a single scratch on it! It had around 10,000km on it I believe (not a single issue other than having to change the inner tube a couple of times). I sold it because I bought the same one but with a different motor – Kingsong replaced the 2,000-watt motor with a 2,200-watt one, which was noticeably torquier.
Funnily enough, the first buyer brought the wheel back the same day, saying that his order from the States eventually arrived or tracking updates that it was now in the country (he mentioned that he ordered the same wheel as he was collecting mine but said that it took long so he asked the seller to cancel the order and buy one from me much cheaper). When he brought it back it had a lot of scratches and torn sides! He even managed to drop it in front of my eyes as he was passing it on to me! So the irony is that it 
was scratch-free after a year of heavy use and he scratched it up completely in a few hours…
Another benefit of having a case is the comfort of riding. I use a case from a New Zealand company roll.nz. It’s soft and has added padding to the sides, which helps a lot with grip and makes holding the wheel quite a bit more comfortably. I still have the same case with my second generation 18XL and both look near new. It also protects the wheel from dust, in addition to making it sturdier when you drop it. You can take it off and wash it or simply tap it to get the dust out after your ride and it looks new again. I love mine. One small inconvenience it that it needs near-constant adjusting in order to aline all the sensor holes. I want it sitting perfectly, however – some other users aren’t so pedantic I’ve noticed. 🙂
Studded footplates are also a must-have in my humble opinion. Footplates in general are arguably the most important part of your wheel because you stand on them and that’s what makes the ride comfortable (or not). So having larger pedals that fully fit your feet is important. First electric unicycles had tiny footplates but with time luckily they duly grew in size (along with the wheels), and 
new age pedals are close to the full length of an average European foot. Studs on footplates directly add to your riding stability. You are a lot less likely to slip off when you hit potholes as well, as in bad weather like rain or snow. In addition to studs, there are those with a honeycomb design. Some are made by the EUC factory-like Inmotion while most are made by the aftermarket enthusiasts. In addition to the above benefits, honeycomb design pedals are also stronger (in most cases and in spite of having holes in them). There is a Polish design and a Russian one. They use different materials (from what I know Russian ones are stronger while the Polish ones are reported to be more comfortable).
Lean pads are completely optional. While some riders stand by theirs, others, like myself, don’t see much need in them. Ultimately, it comes down to your own preference and for that, you need to try them out for yourself. Those in favour claim that they help with faster acceleration and breaking as well as climbing steeper hills. Proponents of more traditional riding styles like myself claim that it does little for them. I tried the Inmotion V11 lean pads as well as others for a week and found that I can accelerate and decelerate better WITHOUT pads.
I had trouble with climbing on some wheels at first until I had a Gotway wheel in China, where you had to push hard in order to go up the Chinese hills. Having had an Inmotion V8 and V10F before that didn’t require any effort at all it was quite a change in riding style for me. Once I learnt however it becomes easy – all you need to do is put weight on the front of the pedals and your EUC will fly off like a sports car. You don’t even need to lean 
for it. I did drag races with people with pads and I won all of them. Of course, it’s not just your skills – your wheel also makes a difference. I can climb any hill that a person with lean pads can on my 84-volt EUCs.
To conclude, at the end of the day it comes down to your technique more than to whether you have installed lean pads or not. If you do want to install them however most people advise using velcro so that you can easily reposition them to find your sweet spot.
Now let’s talk tyres. Changing those makes a difference most of all for when you ride off-road vs on road. There are also tyres however that are better suited for the winter as they have more grip. Generally, off-road tyres have more grip thus are preferred by those who live in the countryside with fewer tarmac roads and more of gravel ones.
The majority of EUCs are shipped with so-called city tyres however since that’s where most riders use their wheels. Changing a tyre isn’t as easy as it is in a car and requires some skill and time. Imagine having to take your car apart to change a tyre!
To add assault to injury, each Electric Unicycle is built differently and requires different screwdrivers and slightly different tools. YouTube is a great source for how to open up your particular wheel. If you are interested in changing your tyre, I would advise to try it first with someone else’s wheel before buying a tyre and investing the hours into changing one only to find that it either doesn’t fit or you just don’t like the ride dynamics of the new tyre you’ve just installed.
Electric unicycles with suspension have shocks in them and some people suggested swapping those out. I’ve not seen any with swapped shocks nor met anyone who’s done it. I also don’t know any other wheel aside from the Kingsong S18 that allows for shock swaps. I can see that it may change the dynamics of it but don’t know enough about the topic to be able to confirm nor deny whether it’s something that’s worth attempting yourself.
Spray painting your wheel or adding stickers or putting wraps can make your wheel more aesthetically pleasing to yourself and make it stand out a bit more. You can also get spray paint for the pedals – I use this black matt paint that works on Inmotion and Kingsong wheels of mine quite well. The pedals look new again for some months after I apply it. Any spray paint or a wrap is highly optional.
Modifications to controllers and firmware are often done to enhance their performance, usually at the cost of safety. Darknessbot, an app for the iPhone, allows you to alter various parts of settings, including lean angle, pedal firmness, perform calibration and firmware upgrades. It also allows setting higher speeds than factory for some wheels. E.g. on Inmotion wheels, you can generally set your speed at around 5 km/h above factory setting, though it doesn’t always seem to work.
With regards to controllers, there are various aftermarket service centres available that will modify your controller for you – normally Gotway, and get more power out of it. This is highly experimental and can be dangerous. A friend of mine had his wheel catch fire near a petrol station. He said that it wasn’t modified but I know that he modifies his controllers so I don’t know for sure. Needless to say, petrol station folks weren’t too pleased – they even considered suing him! Doing this also voids your warranty.
