Let’s talk about assistive devices. Most assistive devices used by people with disabilities are "personal assistive devices" – such as wheelchairs. They belong to the person using them and they are part of that person’s personal space.
So, it's generally inappropriate to lean on or reach over them. Also, it wouldn't be a good practice to restrict anyone from moving around by holding onto the person's personal assistive device.
There are many assistive devices that you won't even notice at first glance, such as a hearing aid. And some aren't used all the time, like a speech amplification device or a white cane.