Hi Bernie,
I'll have a tinker around with one of my other GPS devices. I have two maps to choose from to run in one GPS Device, I had known a Telstra Engineer that created a program that could allow the user to run one or the other, i.e run HERE map or run TomTom. quite a nifty program, the person had passed away about 4 years ago.

I'll make a back up incase things go skewy. I'll let you know if any success.
Cheers.