Does the code inspector look at preexisting work, or only at recent work?
Under the NEC, electricians are held to a very high standard when upgrading systems in existing homes. In many areas, the last electrician to have worked on a system can be held responsible for the whole system.  For this reason, most electricians will be very careful to check for any visible or obvious problems and insist they be corrected before new work is done.
As for building inspectors, they come in all degrees of harshness. Older style electrical work that does not meet current codes, but was and still is safely operational is most always grandfathered and the code enforcement inspector cannot force you to upgrade them unless it effects the new work or presents an imminent hazard. However, if you have substandard or unsafe conditions, any good electrician or inspector are going to point it out and insist on repairing it properly. This is to fulfill their obligation to assure your safety.