The portable installation folder is a folder which you define yourself during the installation process. Nobody else than you can know which folder you defined during installation. The folder C:\Program Files (x86)\Mp3tag with its subfolders is the standard installation folder for 32bit-non portable installations. The MP3Tag-64bit-Version will install in C:\Program Files\MP3Tag. For changing from 32bit to 64 bit installation look here:
Anyway it is not advisable to select a portable installation and then use the standard windows installations folder C:\Program Files or C:\Program Files (x86). Simple users or non elevated users have no write permission to these folders and also should not get them and so spoil this system.
I never experienced that any of my Mp3Tag-installtions overwrote my personal files and settings.
To find your old export-scripts I would simply start a filename-search for these on all drives. Also look for files with the name mp3tagsettings.zip.