What is involved in changing runway/taxiway/approach lighting?
To answer your two questions:


Unless the runway is a very busy one, or the failure is such that it can have an adverse effect on the safety of operations, runways are not closed to replace failed lamps.
Bulbs are not changed in the field, with rare exceptions such as PAPIs. Typically, the maintenance team will have hot spares ready to be installed of every kind of fitting. In the event of a failure, they will replace the whole fitting, which can be done in a few minutes, and replace the bulb at the workshop.


The replacement of a fitting typically involves the isolating of the circuits, untorqueing and disconnection of failed fitting from circuit, connection of new or serviced fitting, torqueing, and powering circuit again.

In the case of PAPIs, the bulbs are replaced on site. The replacement is done by opening the PAPI box, and replacing the halogen bulb.

By the way, bulb changing is becoming obsolete with the wide adoption of LED airfield lighting.