Just switched mine, I am EU citizen and used to hold U.K. EASA ATPL. Straight forward process, the only problem is the U.K. CAA is in quite some mess atm, took me 2 months and approx 2 hrs on phone in total to get all the docs right as they didn’t send any additional info until I called and reminded about myself. But after all docs were sorted 155 form was send whithin a week. Medical took approx 2 weeks.
As I know you can switch between EASA members easily and do not require any additional examination, just doc 155 and medical information. You also do not need to work in the state you’re switching to nor live there. The only problem is posed by German LBA as I heard (purely rumors).
I have never heard of a sim check requirement and I enquired 4 CAA States, maybe I don’t know enough? Can somebody enlighten me? Decided to stop at the CAA I am employed atm in the end, as colleagues can easily help to adjust to a new docs etc. Otherwise the switch process was the same for all CAAs I enquired.