I recently got a call from KDP because I had some requests and it was easier to get a call then do the email thing. At the end of the call, he recommended that I request a call every time I make a significant change or request to my account. If they are the ones doing it, there is less likely a chance of something going sideways later on. He even said that if you have to cancel a pre-order call them and have KDP do it so your pre-order privileges don't get suspended.
In this case, I would recommend requesting a call from KDP and asking them how they want you to handle the transfering of books from one account to another. If there isn't an automated system in place for authors to handle it themselves, then always resort to the call. I've never had a request refused when I was on the phone with them (and I've had some odd requests). If anything, the agents I have spoken to have gone above and beyond the call of duty.
It's also probably important to know that content-review's responsibility has shifted recently (and they don't ever consider the context) which has included being separate from everything else and no contact with authors or publishers. KDP support can't even call them until it gets high enough up the chain. They have to go through emails too. I am assuming content-review will be the ones checking this and having someone from KDP who can contact content-review on your behalf to help put things in context can only help and not hurt.
In this case, I would ask, is there any harm from reaching out the KDP first? Since I see the answer as being no, I would recommend that option. Doing it yourself and hoping content-review doesn't act first and ask questions later is a potential issue. (For reference, I had a title appropriate to my genre, but included a single word that raised flags with content-review for print. It took 4+ days before support contacted me and said the problem had been fixed and that I wouldn't have any more problems because it had been noted in my account in big bold letters.) The phone call costs you nothing but time and you'll know that you're covered from any super strict content-review person who acts without looking at the entire picture and making a decision based on context.