You can book a taxi via following methods:
Online: http://airports4less.net/
Telephone: +44 160 349 0150
Yes, it's possible to pre-book a taxi with Airports 4 Less, please contact the company.
Airports 4 Less has both regular and air-conditioned taxis, please mention your preference at the time of booking.
Please contact the company on their helpline number to make any changes.
Generally drivers will meet the passengers at the arrivals on airport pick ups but do check with the company.