If we're talking about minor adjustments it should not matter imo. I mean, would tuning your bass temporally to a half step up or down mess up your neck? I don't think so. So if you need to tighten the truss rod while the bass is in tune, unless it is a drastic adjustment, it should not matter as your bass will be tuned probably less then a half step up at the end of the adjustment. You should never do drastic turns anyway and since you have to tune your bass every time you make an adjustment, you're safe.