There is a way to keep the packages folder by copying it to another drive or folder.
Then uninstall MSFS.
Then install again by setting up the location in the installer. Let it start downloading so it sets up directory structures. So basically, let it download one or 2 files and decompress them. Then pause the installer and exit.
Then copy back the package folders saved before uninstall. Then relaunch MSFS and it will detect that packages are there.
However, if you have a fast internet connection, if it were me doing this, I’d be clean installing. 