[EC900]

I’m not sure about the ‘72 - but I was able to wiggle my tach out enough to swap bulbs with steering wheel still in place.
I was able to lift the dash pad slightly and ease it out. It’s tight but doable.
And if you can slide the rubber ring back to get a little extra wiggle room.

Yes, you simply reversed the bulb sockets and if your fingers are slim enough you maybe be able to reach in and swap sockets by just tilting each side to access socket should do it.
Test operation before putting it back.

+ One note about the cover I found but didn’t bother was that there are two screws on either side of the housing I’m not sure if removing these will release the clamshell cover halves.