My experience
Well I faced this situation from the outside at one point.
It was with my X-and her new boyfriend held her down and put an ax to her throat and he threw her around and what not. To this day I don't know the true story necessarily, though I suspect from the guys history this is the truth.
Anywho, she had second thoughts about the ax murderer so she said she made it all up (they had pictures of the bruises and everything). She said she got them at a fight in a bar with a stripper, and she was just scared and didn't want to tell that true story cause she didn't want to lose our kids (we were going through divorce at the time and she had a no alcohol thing going). So she was scared and made it all up to cover up the bar fight and drinking (this all does have a point for you by the way so wait for it
).
If you think about the second story, it makes NO sense what so ever. The cops were not at the bar. No one would have ever found out about a fight with a stripper. In reality (I think) she did get in the fight with her BF, and because she was scared of what he would do for her telling on him, and they have a kid together too, it was too much so she said the heck with it.
She did not drop the charges, as mentioned I don't think you can do that. She just lied and said none of it really happened and made up the second story (once again guessing, but we).
She was charged with purgery, but they did drop the case against him.
So you could just lie, and make up any old lame story you want really, and it won't stick in my experience. You will however likely be charged with purgery. She ended up with 1 week of house arrest and like a 400 some dollar fine I think. HOWEVER, purgery is generally much more serious than this, at least in theory, you could end up with a not so small slap on the wrist so take what happened here with a grain of salt.
Keep in mind she also reportedly hit him during this whole thing as well, for what it is worth.
So if you really want him out of trouble, you could lie about the whole thing in court. Right wrong or indifferent, I'm just saying, and I have seen nothing but lies in court anyway
Like you, this will contradict your prior police statement, and YOU may get in trouble.
Sorry for the long windedness, but hope this helped.