I have just found a very easy way to reset your rank back to recruit.
On the main title screen R6V2 bring up your blade and press X to sign out of your account.
Then press start it will warn you that you will not be able to save any progress
Press B to return to the main title screen
Press the guide button to bring up the sign in blade and sign back in to your account.As soon as your signed in quickly press the guide button to remove the blade and quickly press start.
If you have timed this correctly you will again be warned about not being able to save and your rank will be reset.
Please note : I took me a few tries to get the timing right as sometimes it will fully load your profile just sign out again. Also my game froze for a few seconds on the screen saying I would be unable to save progress just be patient it was only about 20 seconds.
Also for some strange reason im still able to use the guns I had unlocked although my ACES have been reset.
Any questions send me a message
Gamerscore hero - New target 100k