problem to change tuning strings in Tab

Detailed steps and sample score needed, I can change string tuning on a tablature staff in 3.0.5 without any problem

There's no string data in staff properties, not all by itself, only on staves of scores with plucked string instruments, so there are definitly steps missing in your procedure.
Creating a new score from the Guitar +Tab template and then going to staff properties > string data > changing any string's pitch, pressing OK twice... no crash

I do get a crash though when entering notes into such a changed pitch staff, above a certain pitch (more investigation needed). In 3.0.5 and 3.1RC. Might be related or a completly different issue.

@Greenpablo:

Can we please restart from the beginning. Things are missing for the understanding of what you are observing.
A few questions first:
1) Which version exactly do you use? (to check, go to menu "Help"/About)
2) Do you use one of your existing scores? If so, it would really be useful if not necessary to attach it here for verification.
3) Or are you talking about something that happens with any new score created. And if so, do you simply use a Tablature staff (for example, the template in the Wizard), or the Guitar + Tablature template (with linked staves)?
4) Finally, with regard to the steps you describe in a previous comment, what exactly do you mean by "Open height"? (I guess something related with "Open" string - but what you do exactly, one open string ou more etc..)

Update to 3.0.5, there is no reason at all to stay with 3.0.2.
Then check again

You want to change the E4 to a D4? Works with 3.0.5, at least for me

I get some crashes, but very few, and I can't reproduce for the moment from a certain sequence of steps that would cause a systematic crash.
In any case, and even if I don't know right now if it is the main culprit (I would say possibly, a data update which fails somewhere and with a specific sequence of steps, e.g. possibly related to :#285274: changing a guitar's string data pretends to update the instrument's range, but does no ? ), you should avoid to tick "open string" for D2.

This is a totally misunderstood feature, and completely useless for guitars. It is only useful for lutes that have extra basses outside the fingerboard. I still think it's a feature that has extreme visibility for truly confidential use cases. IMHO, it should be elsewhere, really more hidden, and that would perhaps avoid (I'm not sure yet) this kind of problem.

@Jojo. The sixth string in guitar, it is the lowest string (E2, therefore towards D2, as on the user's image - Re2), and not the highest open string (ie E4).
Like a violin, for example, the "chanterelle" (you sing on it, the melody on it), is the thinnest string, named as first string.

A 7-string guitar (standard & Tablature) is already available in the wizard. Type simply "guitar" in the search box.

And for the issue/crash, of course, if you have a very detailed sequence of steps to reproduce it (I insist, very detailed, each click or each action in a specific order may be decisive), feel free to share here.

we still don't know how to reproduce and it is not an issue with some development version but (started) with MuseScore 3.0

You only see common instruments, switch to all