Oops

In reviewing the post your question was not really answered: did they change lamps or change lenses. Where's a real steam engineman for the bad old days when you need him. I don't really know because I never had to do it, the diesels had a different arrangement. Either way was probably a possibility. Usually a train would run from one terminal to the next with the same signals, so there may have well been a room full of class lights with white and green lenses at the terminals. On the diesels on the SP we changed lenses, but there were only two to change, not eight. On some diesels the lenses were permanently mounted and you turned lights on or off behind the appropriate color.
So even my long winded post doesn't really answer you question.