What are looking for are not groups. Every sprite will be assembled and OAM is used to display sprites on screen. In case of CV you like to figure the sprite assembly format and change them for every object and every frame you like to have a different palette assigned.
Here is the format:
1 2 3 4 NextBlock??
Object Assembly Format: 08 F0 D0 03 E8 F1 D2 F0 F1 D4 F8 11 D6 F8 F0D44300F1D208F1D01011D600
AA BC DD EF GG BC DD GG BC DD GG BC DD GG
AA= Number of 1x2 SpriteBlocks used for the Frame
B= Ypos 8 pixel
C= Ypos pixel and uneven number will mirror and break palette. Also it will alternate to the next SpriteBlock
DD= CHR Slot Number (Only Even Numbers Work Spite)
E= O+1=Normal 4+5=Mirror 8+9=Flip c+d=MirrorFlip (For Block "4 Times 1x2")
F= Palette 0-3 Then it will repeat cycling Palettes
The Sprite assembly table is stored at the very first bank of the PRG ROM. I would command to use mesen to do this changes. In the Memory editor you can save the ROM or the changes as IPS.
The workflow is as follow:
Get on screen what you like to change. Press pause and do a savestate. When reloading the game (assuming you don't save usage table to disk.)
Then just load the savestate. Since you paused, the game only shows the current assembly on screen. This is highlighted blue in the memory editor and easy to find like this.