US Armed Forces - Americas
No, you never get your basic tech back. You can only replace the researched tech with another tech.
I think you mis-read what I wrote. I said that "Once a card as been researched..." Your basic tech is not a card. All cards that you research into techs can only be changed by researching again, removing the first tech, and adding the new one. Your basic tech will never be open for use again once it has been changed.