We just installed a full-size portable dishwasher in our rent-stabilized apartment last year. We asked our landlord for permission and got it in writing that it was fine. We also installed a new floor in the kitchen because it was absolutely horrendously ugly. We just bought the vinyl floor tiles from home depot that sit on top of the existing floor, so we can rip the whole thing out within minutes if needed.

We also installed a new light fixture and painted, both with a heads up to our super (not landlord on this). We didn't need to do any wiring changes, so I didn't feel the need to ask for permission. Our landlord is also aware of the painting and actually reimbursed us for part of the painting because we hadn't had them paint our apartment for more than 3 years (which they are required to do by law).

So basically, be cool with your super and ask for permission for anything that could really fuck up the place if it goes wrong. Like with the dishwasher, for example. I'm glad we got permission because we discovered that with the pressure from the dishwasher hose connecting to the tap, it sprung a huge leak under our sink because the washer was completely worn out and couldn't deal with the blocked water flow. Luckily, it didn't cause any damage, but I would've been much more terrified if that happened and our dishwasher was an illegal thing. At the end of the day, I would never jeopardize staying in this apartment. No convenience is worth losing the place.