I've been asked to play a gig where one of the tunes is Breaking Benjamin's "I Will Not Bow." The bass tabs I find show the tuning for a 5-string is (low to high) Bb - F - Bb - Eb - Ab . I'm wondering about the strings that have to be tuned up 1/2 step. I'll be playing it on an Ibanez SR406 6-string. Since this is a one-off gig, I don't want to have to take the ax to a luthier for setup or have to buy a new set of strings. If I change the tuning for the gig and then put it back to "normal" afterward, will I damage my bass?
It’s hard to say definitively, but it’s unlikely that tuning a half step higher would do any damage. The main element of a bass that takes the tension is the truss rod, and if you were to keep a bass in this tuning it would probably be wise to adjust the truss rod to give a little more back-bow, ie get it working a bit harder against the tension. Without a truss rod, the wood of the neck would bend a fair bit even at standard tuning and more for higher, and probably make the bass deformed beyond what fretwork and so on could amend quite quickly. So the truss rod is what holds the tension of a standard tuned bass, and it is strong enough to hold the neck of the bass at higher tension tunings too.
The bit where it’s hard to say for sure is ‘will an increase in tension across all strings counter-act the trussrod enough to REQUIRE the truss rod to be set at a different setting to avoid wood damage’. I would say for one semitone you would probably be well within the strength of the truss rod to counter before any damage occurs. I’m pretty confident it will just manifest as a slightly more bowed neck, and a slightly higher action in parts of the neck, for the duration of that tuning.
It will depend on the thickness of the neck itself and potentially the size of the truss rod, but the range of preferences for normal, damage free, neck setup is quite a bit greater than the extra bow created by a one semitone increase in tension. In other words your neck will bow a bit, but all within the range of what could be considered a normal setup choice.
If you have a very thin neck or a budget bass you may want to pay a bit more attention to how much it bows under the greater tension tuning. If you get a WAY higher action then it’s still PROBABLY fine but something to keep more of an eye on.
If the action goes up a little but otherwise much the same, I think you’ll be all good.
One caveat to alternate tunings and bass range is if you regularly detune ONE string, ie in drop D, then that can, over time, cause the neck to twist a bit, making further setups hard to get right. I had this with a Warwick streamer, the imbalance of tension caused the neck to go ‘out of true’, not to the point it was bad to play, but enough for me to designate it was my ‘drop d’ bass. This was fairly minor, even after years of leaving it in drop d, but it is a consideration if you want to preserve the best possible setup of a bass and integrity of neck. I would guess that if I had returned the low d to e after each practice/gig it would have mitigated any problem, and even with this unbalanced tension the change was very very minor, with the bass still playing well to this day.
Even if this was the tuning on a standard 5 string, it won't be detrimental. For a start, different gauge strings are available, so even with standard tuning, a bass can end up with different tensions.
Then there's the gadget that can alter the tuning of a string by means of a cam (fixed in place of a normal machine head) that is designed to change tuning. Hipshot, I think. Those don't appear to be responsible for damage to bass necks.
So go ahead without worry. If you still have concerns, why not simply re-tune for that one particular number, or have another bass that's ready tuned. It's only for a couple of hours, surely?