chown/chmod/chgrp on Users/____/Library without disabling SIP?
First, of all you do not need 4 cycles. To enable SIP, you can enter the command below, then restart the Mac.

csrutil clear


You should get the message shown below.

Successfully cleared System Integrity Protection. Please restart the machine for the changes to take effect.


You can disable SIP on a single restart, if you install rEFInd. If properly installed, you can select rEFInd from the Mac Startup Manager. From the rEFInd menu, you can disable SIP and then boot to macOS.

So to summarize, you can enable or disable SIP though a single restart. So the total number of cycles can be reduced from 4 to a  total of 2.

As for coping files from one users account to another, I do know were SIP is involved. If one of the accounts has administrator privileges, then you can enter the command below to become the root user.

sudo bash


Once you are the root user, you can enter the necessary commands to copy files between accounts. 

Personally, I do not employ the root user. I just use the Finder application. I move (or copy) the files to the Public folder of one account, then switch users and copy the files from the Public folder to the other account.