The commands (pkexec and sudo -i) in and of themselves aren't necessarily harmful. However they do different things in terms of granting permissions to apps.
The sudo ("substitute user do") command allows you to run a process as another user, typically the root user. That is, by default it runs the process as a user with unlimited power.
When you use ...
According to pkexec man:
The environment that PROGRAM will run it, will be set to a minimal
known and safe environment in order to avoid injecting code through
LD_LIBRARY_PATH or similar mechanisms. In addition the PKEXEC_UID
environment variable is set to the user id of the process invoking
pkexec. As a result, pkexec will not allow you to run ...
You can right-click on the Files icon in the dock and select New Window As Administrator from the menu. Once the window has opened you can paste your folder there.
Or you can do it in a terminal with sudo as well:
sudo mv original_folder /usr/share/themes