Service Contracts

Hi,

If I had a service contract for 2,000 units and i scheduled some more flights from that same airport would i be able to increase the capacity of that contract or would i have to get a new one.  Additionally,if i have 2 contracts one for 2000 units and another one for 500 units but the contract with 2000 units is overbooked would the over booked amount be automatically transferred to any availible capacity in the 500 unit contract or would it be subject to AS standard handling . i am asking this because i was trying to assign different service contracts to different flights and i just cant divide them equally between the service contracts. Lastly, if i were to cancel 2 contracts one 2000 and one 500 and get a new contract for 2500 would the terminated contracts still be in service till the next billing date or do they stop operations immediately. any tips and tricks on how to get over  this problem?? Thanks