1. Yes but the provider cant give you the code as it may be in multiple systems. Would you want a security system provider that didn't care about protecting their clients. They will have to attend and change it and this would be a chargable call.
2. If diy then then default codes will be supplied
Any decent installer would not allow engineer access etc during warranty or service period imho. There would be a charge to call out and reset the installer code at the end of that period etc