As the owner of both a DeArmond and a Guild, I can say that the signal strength from the Guild un-preamped is pretty minimal and unimpressive, and amplified is not as great as the DeArmond. This is probably a combination of a lesser output from the pickup on the Guild, compared to the DeArmond, and not so much boost in the preamp. The pickup and the preamp on the DeArmond are better than the Guild in terms of output and EQ.
So I would reckon that an un preamped Dearmond pickup should have a bit more output than the Guild but is it usable? I think you would still need an external preamp or a high gain on your power amp. With that in mind a bypass switch should not be difficult to install - put simply it would just disconnect the pickup from the input to the preamp, and switch it directly to the output jack.