Help! me go from CM12.1 >stock >straight talk. (Not a noob)

I won an HTC One M9 from sprint. My previous phone was a non-triband L720 Samsung S4.
I'm selling the phone to a friend who will be getting Sprint, but can't yet do it because the closest place around is like 60 miles away!

So in the mean time, he got a straight talk card (CDMA&GSM)
I have found two relevant URLs pertaining to unlocking the phone.
Domestic unlock - http://forum.xda-developers.com/show....php?t=2530610
And international - http://forum.xda-developers.com/show....php?t=2415587

Thing is,
A. I'm in good standing with Sprint so I can get it unlocked.
B. Dear god look at those instructions! I can unlock it manually, but dang man! That's scary if I go into a menu and screw things up, or worse, it doesn't unlock and I don't even know which step I messed up on. I've been flashing for years, I'm not a newbie.

I need help with:
A. helping me know which stock from to flash. I came from lollipop.
B. while keeping my recovery if possible. He wants my CM12.1, so I will back it up and then restore it.
C. Do I need to flash any modems/basebands? I'm confused. I have
L720PUGOD2 currently.

So
1. Backup cm12.1
2. flash lollipop stock
3.call Sprint, get UICC unlock
they will domestic unlock it right?
4. Then I can get back to the cm12.1 on my own.
Is that correct? From what I read, CDMA straight talk
So hopefully it's that easy. My buddy want the phone working asap so I would really appreciate an opinion from a pro. Thanks!