I have a lot of FR guitars and none of them could be tuned to Drop D with the fine tuners, might be possible if the fine tuner is fully at the "in" position for E standard. Prepare for major re-tuning the other strings. Unlock the nut and tune away... Anyways tuning to Drop D shouldn't require to change the spring tension. I guess that starts to be a problem with Eb or D standard. I use multiple guitars each with its own tuning (and one with fixed bridge for non-standard tunings), problem solved.
