Most of third-party themes come with some rearrangement of the default modules positions and/or some extra modules of their own.
Our themes too.
So you will lose (partially or totally) the configuration of your previous theme but, if your previous theme has been coded properly (with a correct configuration file), you will be able to restore it with just a clic.
As always, before installing a new theme, a backup is always suggested.
Last Updated: 29 Oct 2019