I seem to recall that for years Marin listed Medium as the gauge of choice for their "D" size guitars. Unless the new tunings put greater tension on the top of the guitar I fail to see where retuning an instrument will do significant damage to a top.

I have always used Silk and Steel strings on my Martin 0-16 NY but the repair shop at Martin told me I could put Bronze Light gauge wires on it without damage to the guitar.

I would ask the luthiers in the group if the tension required to damage a guitar is a total all the strings? Or can changinging one string to a greater tension be enough to damage a top?