It causes that card to also be treated as a Digimon with X000 DP. For example, if a Tamer is also treated as a Digimon, it can attack like a standard Digimon, and it will gain inherited effects from cards stacked under it. However, even if a Tamer is played and then treated as a Digimon in the same turn, it can't attack during that turn.

No, it is treated as both a Digimon and a Tamer.

Yes, it's treated as an effect of both. Because the card is treated as both a Digimon and a Tamer, the activated effect is treated as both a Digimon effect and a Tamer effect.

Yes, it's deleted upon the rule check timing.

If an effect has triggered and the card is affected by a "is also treated as a Digimon with X000 DP" effect, the play cost, level, and DP are overwritten by the newer effect. However, if an effect has already activated and the card is affected by a "is also treated as a Digimon with X000 DP" effect, the already activated effect will be overwritten. Any other effects such as <Rush> that are later gained will be added.

Yes, you can. When an effect is activated on a card that's treated as both a Digimon and a Tamer, the effect is treated as both a Digimon effect and a Tamer effect, therefore you can gain memory.

No, it won't be affected by effects. When an effect is activated on a card that's treated as both a Digimon and a Tamer, the effect is treated as both a Digimon effect and a Tamer effect, therefore the chosen opponent Digimon won't be affected by effects.