Q1: I chose 1 opponent's Digimon with a play cost of 8 or less as the target for "can't attack players" in this card's When Digivolving effect. If that opponent's Digimon digivolves during their next turn and becomes a Digimon with a play cost of 9 or more, can it now attack players?
No, it can't. Even if a target Digimon of this card's When Digivolving effect becomes a level 9 or higher Digimon, it can't attack players.
Lv.5 Infermon BT17-055 C Ultimate | Unknown | Unidentified [When Digivolving] <De-Digivolve 1> 1 of your opponent's Digimon. Then, 1 of their Digimon with a play cost of 8 or less can't attack players until the end of their turn. --- Inherited: [All Turns] [Once Per Turn] When another of your Digimon with [Diaboromon] in its name is played, <De-Digivolve 1> 1 of your opponent's Digimon.
Lv.5 Infermon BT17-055 C Ultimate | Unknown | Unidentified [When Digivolving] <De-Digivolve 1> 1 of your opponent's Digimon. Then, 1 of their Digimon with a play cost of 8 or less can't attack players until the end of their turn. --- Inherited: [All Turns] [Once Per Turn] When another of your Digimon with [Diaboromon] in its name is played, <De-Digivolve 1> 1 of your opponent's Digimon.
Lv.5 Infermon BT17-055 C Ultimate | Unknown | Unidentified [When Digivolving] <De-Digivolve 1> 1 of your opponent's Digimon. Then, 1 of your opponent's Digimon with a play cost 8 or less can't attack players until the end of their turn. --- Inherited: [All Turns] [Once Per Turn] When you play another Digimon with [Diaboromon] in its name, <De-Digivolve 1> 1 of your opponent's Digimon.
Lv.5 インフェルモン BT17-055 C 完全体 | 不明 | 種族不明 【進化時】相手のデジモン1体を≪退化1≫。その後、相手のターン終了まで、登場コスト8以下の相手のデジモン1体はプレイヤーにアタックできない。 --- Inherited: 【お互いのターン】[ターンに1回]名称に「ディアボロモン」を含む他の自分のデジモンが登場したとき、相手のデジモン1体を≪退化1≫。