This is the 16296th most frequent Russian word.
регистрационных
"Registration" or "related to registration."
Here, 'регистрационных' relates to 'данных' (data) and signifies that the data in question pertains to registration purposes.
Вам нужно заполнить форму для регистрации регистрационных данных.
You need to fill out a form for registering registration data.
In this sentence, 'регистрационных' qualifies 'номеров' (numbers), indicating that these numbers are related to the registration of the vehicle.
Регистрационных номеров автомобиля не удалось найти в базе данных.
The registration numbers of the car could not be found in the database.
The word 'регистрационных' describes 'изменений' (changes), indicating that the changes are in regard to registration records or similar formalities.