Nothing is straight forward with a Traction as you will find out 🙂
The centre boss will depend on which wheel is fitted, if a standard Citroen one, try turning the centre anti clockwise and see if it comes loose. Simply levering it out may damage it.
On an aftermarket ‘Quillery’ wheel the centre boss is like a horn push and spring loaded so push in and turn slightly anti clockwise and it should pop up.
Why fit a smaller steering wheel though, for access?
It will probably have a rotary control added so you can wind the power down (the few I have seen have one) so you can wind the power off when rolling along. I have considered having one fitted but other items needing attention have swallowed up any funds that may have been available to do it…..