I tried it now, and I could switch to notepad and then paste the Serial Number.
However, the paste works only if you right-click on the serial number field and select "Paste" from the menu. It doesn't take the usual keyboard shortcuts like CTRL+V or CTRL+Ins normally associated with Paste.
However, none of this was required, if you just used the .REG file which was created in your "home" (the folder with your name, usually under C:\Users\YOURNAME ) because, the whole point of the .REG file, was to prevent you from having to type the Serial Number manually.
So, the fastest and more foolproof way to reinstall, if you have your existing .REG file (we assume you don't trash your own home folder when reinstalling the system, and do a backup...) is:
- With the sim closed, double-click the .REG file, for example FSDreamTeam_ZurichX.REG, located under C:\Users\YOURNAME
- Confirm you want to insert it in the registry.
- Start the sim, it will ask if you want to reactivate Zurich, just say YES, no manual serial input required.