This is usually doable until it's DEWS/SAGE radar code from the 50's. That's what NASA started with and the last guy died in the 90s. We got every other subsystem off the mainframe, but had to keep it around for the radar stuff until 2004 or so.
WEX/Display builder/etc:
Even when I was there my young peers weren't too keen on legacy/back-end understanding. GUIs were the cool thing. I worked on something that touched many legacy subsystems so got to work with a lot of "dinosaurs" (what the Pirates called them).
MCC testing was all AM shift, pirates/youts up front, retired controllers in the back. Test MOC took 30 minutes to recycle. I always sat in back if they'd let me.
