If I have a longer magazine and chamber for a given round and the reloading manual calls for 60 grains of powder maximum for a given OAL, if I am able to make the OAL thirty thousands longer, can I safely add more powder?

The simple answer is no. Just because you have more case capacity does not mean you can fill the void with more powder. If the book says 60 grains, at 58 grains I begin inspecting each fired case for pressure signs. 60 grains is an estimated max. Each gun is different. I have had loads that show pressure signs before book maxes. If your bullet is touching the lands theoritically the pressure will be higher any anyway.

So the long answer would be if you have zero pressure signs at the current OAL then checkit after you increase the OAL. If still no signs, then gradually increase powder in half grain increments. But you gotta be careful. Pressure signs, serious ones, can suddenly appear with no pre warning.

If it were me, whatever shot best before published max would be the load I use. Not sure what your trying gain there.

Dead on Earl. The magazine length should not be used for pressure adventures. The cat should check he's not going into the lands, otherwise he should maybe reduce the load as you said.

Thank you for your astute information gentlemen.