Simply rename it?
12GB ???
I am not surprised you can't open it!!! You may need to enable a LOT of scratch disk space.
Where on earth did you obtain an image of that size? It would have to be in BigTIFF format surely.
My largest EVER TIF file was about 4GB (packbit) and even that was a nightmare to manipulate.
I would not expect MAPC2MAPC to open it even with VS enabled.

Or do you mean 12MB?