Crew seating is partly concerned with the regulations requiring a crew member next to certain exits. Airlines choose different combinations of seating based on class and galley/lavatory arrangements and this changes the number of required exits and crew required to sit next to the exits. Some long hall airlines require berths for crew rest and sleep - I imagine some airlines may have employee union requirements.
All this requires ongoing customized cabin arrangements. Airlines often change the seating during mandatory maintenance (a, b, and c checks) to accommodate different routes, cultural expectations and changing economy.
Interestingly, the cockpit itself may vary. According to FAA regulations large aircraft must have at least one observer seat (usually called a "jump seat"). But, I have seen cockpit options that vary the number and type of "jump seat" in the triple 7.
For example, one cockpit of a Boeing 777 offered two padded conventional seats or three fold down "bench" type seats. I guess one company wanted the FAA observer to fall asleep and another company wanted to discourage "observers".