If I use this option on a Digimon which is later de-digivolved into a Tamer, will my opponent be able to delete that Tamer with an effect on their turn?

No, the "can't be deleted by your opponent's effects" part of this card's effect still applies whether the target of the option is now a Tamer or a Digimon.

Defense Plug-In C rulings (BT10-105)

1 official ruling from Bandai. Straight answers to how this card actually resolves.

Effect: While you have a Tamer, you can ignore this card's color requirements. [Main] Until the end of your opponent's turn, 1 of your Digimon gains Blocker , Reboot , and can't be deleted by your opponent's effects.
Security effect: [Security] Reveal the top 3 cards of your deck. You may play 1 Digimon card with a play cost of 4 or less among them without paying its memory cost. Place the rest at the bottom of your deck in any order. Then, add this card to its owner's hand.

Official Q&A

If I use this option on a Digimon which is later de-digivolved into a Tamer, will my opponent be able to delete that Tamer with an effect on their turn?
No, the "can't be deleted by your opponent's effects" part of this card's effect still applies whether the target of the option is now a Tamer or a Digimon.

Got a line that uses Defense Plug-In C? Map it in the builder and share it with a link.

Questions and answers are Bandai's official rulings, collected and translated by the DigimonCardGame Wiki community and reused here under CC BY-SA. Card names and card text are © their respective publishers; Combalo is not affiliated with Bandai.

Defense Plug-In C rulings (BT10-105)

1 official ruling from Bandai. Straight answers to how this card actually resolves.

Effect: While you have a Tamer, you can ignore this card's color requirements. [Main] Until the end of your opponent's turn, 1 of your Digimon gains Blocker , Reboot , and can't be deleted by your opponent's effects.
Security effect: [Security] Reveal the top 3 cards of your deck. You may play 1 Digimon card with a play cost of 4 or less among them without paying its memory cost. Place the rest at the bottom of your deck in any order. Then, add this card to its owner's hand.

Official Q&A

If I use this option on a Digimon which is later de-digivolved into a Tamer, will my opponent be able to delete that Tamer with an effect on their turn?
No, the "can't be deleted by your opponent's effects" part of this card's effect still applies whether the target of the option is now a Tamer or a Digimon.

Got a line that uses Defense Plug-In C? Map it in the builder and share it with a link.