Plenty of players want the flexibility of alternate tunings without owning a separate guitar for each one. It's entirely possible to set a single guitar up to handle a couple of different tunings reasonably well, as long as you understand the trade-offs involved.

Why tuning changes affect setup

Every element of a guitar's setup, action, relief, intonation, is calibrated around a specific string tension. Change the tuning significantly and you change the overall tension pulling on the neck, which can shift the action and relief slightly, even if you haven't touched the truss rod.

Small tuning changes are usually fine

Something like Drop D, which only affects one string and doesn't hugely change overall tension, is generally fine on a guitar set up for standard tuning, though the dropped string may benefit from a slightly heavier gauge to avoid excess buzz.

Bigger changes need more consideration

Tunings that drop the whole guitar significantly, or open tunings with unusual tension distribution across the strings, have a bigger cumulative effect. If you're regularly switching into and out of a tuning like this, your guitar's setup is essentially a compromise between two different tension profiles, and it may never feel quite as dialled-in in either tuning as a guitar set up specifically for just one.

Practical approaches

• A dedicated capo-friendly setup. If you mostly use a capo to change key rather than true alternate tunings, this has minimal impact on setup and isn't something to worry about.
• A "good enough" compromise setup. For occasional alternate tuning use, a competent setup can find a reasonable middle ground that plays acceptably well in both, even if it's not optimised for either.
• A second guitar. For a tuning you use constantly, such as a dedicated Drop D or open-tuning guitar for slide playing, a second instrument set up specifically for that tuning avoids the compromise altogether, and is what a lot of gigging players end up doing.

Getting it right

If you're regularly moving between tunings on one guitar and it's never quite felt right in either, that's worth mentioning when you bring it in for a setup. A good tech can find a genuinely usable compromise, or talk you through whether a second, dedicated instrument makes more sense for how you actually play.