V2 Update
Added Owner Room support, thanks avenger54

Owner Room support
Now you can change the variation of each girl separately in the Owner Room.
But they cannot wearing exactly the same costume.
You can check on my Suit ID list for my mod below to find which costume is independent.
https://www.loverslab.com/topic/114640-doaxvv-minazukis-mod/?do=findComment&comment=2488435

Due to the owner room support, now you need to press Ctrl + 1 or Ctrl + 2 to turn on/off the variation switch. (default is off)
It will show an OSD on the bottom-left corner to tell you the variation is on or off.
If it is showing on, you can press the key to change the variation.
Just set one girl to on, one girl to off, and you can change the variation separately.
If there's only one single girl on scene, you also need to press Ctrl + 1 or Ctrl + 2 to switch on the variation in order to change the variation.

Variation
Press X to cycle between the top.