Satan is bound, and has been left impotent, as per scripture.
So even though he is already bound he was doing the following at the time when Paul wrote his second epistle to the church at Corinth?:
"for Satan himself is transformed into an angel of light."
As I said earlier, the Greek word translated "is transformed" is in the present tense. In
The Blue Letter Bible we read the following meaning of the present tense:
"The present tense represents a simple statement of fact or reality viewed as occurring in actual time. In most cases this corresponds directly with the English present tense."
So at the time when Paul wrote this epistle Satam was transformed into an angel of light. That is what is meant by being "viewed as occurring in actual time." According to you Satan was doing that when He was bound in the Abyss.
Satan will not be bound until the following happens at the battle of Armageddon (Rev.16:13-16):
"And I saw an angel coming down out of heaven, having the key to the Abyss and holding in his hand a great chain. He seized the dragon, that ancient serpent, who is the devil, or Satan, and bound him for a thousand years. He threw him into the Abyss, and locked and sealed it over him, to keep him from deceiving the nations anymore until the thousand years were ended" (Rev.20:1-3).