If you are talking VC panels, it is hard, if not impossible. I could be full of it here but....As I understand it, the VC panel bitmap image is hard wired in the MDL file. You may be able use a different image file by naming it the same as the existing VC image file. However, the new file may not match.
2D panels are easy to create using the technique dhazelgrove explained. You can even use gauges from other aircraft (most of the time) by adding the path and name of the new gauge in place of the existing gauge.
Hope this helps,