Sometimes the sudden attitude change is caused by the iguana's previous stone-cold fear of you that made him hold still, even often lets you pet it. When it closes it's eyes, it's shutting you out because of fear. It is not dreamy enjoyment caused by your rubbing and petting. Then when it looses the fear, it will revert to normal stress behavior that most igs do when their habitat/.owner is changed. That includes many behaviors such as poop painting, attacking it's owner and running madly around in their habitat.
Your ig has some strength now, so he can break or cut your skin when he bites. There are ways to prevent that. First, when he tail-whips you or bites you, give no signal that it bothers you at all. If you do, he may remember his trick forever. That certainly does not come naturally to humans. But you have to use your brain to counter his impulse to attack you.
You need to pick him up every day, so throw a small towel over him and instantly reach in and pull him out of the cage, then move to neutral territory. Press him against your belly and let him do his alligator rolls. But don't let him escape. The alligator rolls will last about 30 seconds. Then just sit in a chair with him in your lap, for about 15 minutes. Then gently put him back in his habitat. When he realizes he is returning to his claimed habitat he might start to struggle hard. Your response to that is to hold him firmly enough, don't let him slap the cage with his tail (that sometimes cause tail breaks).
When you want to pick him up, remember to lower your hands to the substrate and go after him from his side. Don't move anything around above his head, as he is genetically programmed to be afraid of hawks.
This step ends when he voluntarily stays on your lap. He likes the feel of your warmth and you feed him his favorite treats there.
The next step is to train yourself and him to free-roam in your house. It's a fairly complicated subject.
Please stay in touch,