Label Actions Using Technical terms or "Plain Word" terms

I am working with an organization that is redesigning software created roughly 15 years ago. At the time the software was very technical, with form labels that exactly match database column titles (ex: Dev_Cmd for Device Commands) and selections or buttons titled to exactly match the name of the service being called (ex: CallHistC() for Call History Command).

As we redesign the software, we believed it would be important to have more user-friendly terms for these various titles and commands. We brought this up with our Customer Support team and met resistance to this change; they insist users know these terms and the user-friendly terminology would cause confusion and may be ambiguous.

Is it a mistake to change terminology if a current customer base is familiar with it?

What is the best way to determine if "plain word" terminology would be an advantage or disadvantage for users? I would like to avoid change resistance and I'm concerned a customer survey would be skewed toward expert users.