changing globals possible?

I’m I right, that you can change a global from text to integer, without worrying that this goes wrong, with a next update by a customer?
(Like with a normal-field!)

(I have not the right tools yet, here to test it!)

Correct, type is used for validating relations, but you better comply to the type you specified.

Yes, but if I change a global from Text to Integer, and my customer does an update, is this global than changed from Text to Integer too?

I do not understand your last question, please explain in more detail.

What I main is:

let say I have a global TEXT
and than install my solution to a customer

than I change the global (on my developer-machine) to INTEGER and export the solution.

My customer imports the solution. Is his global now changed to INTEGER too?

yes :-) otherwise it whould be a bug