I can now manually load the MAME 2016 (0.174) core in Retroarch.
But it's a long trip.
In Batocera's setup go to Games Settings > Advanced > Mame.
Set Emulator to "auto" and Core to "auto".
Try to start any game (retry until you get a game starting).
Then press HOME + A buttons simultaneously to access Retroarch's setup.
In the Retroarch's menu, go down to Overrides. And make "Save Content Directory Overrides".
Retroarch will create a MAME config.
Go to "/userdata/system/.config/retroarch/config/MAME 2003-Plus" directory of your Batocera file system.
Then edit the file named "mame.cfg" and add this 3 lines and save :
menu_show_load_core = "true"
menu_show_online_updater = "true"
menu_show_load_content = "true"
Now you can access online update's options in Retroarch's setup.
So. Start again the game you launched previously. And press HOME + A buttons simultaneously to access Retroarch's setup. Press B button to go back. And go to Load Core > Download a Core.
Search for "mame2016_libretro.so.zip" and download it.
After auto-extracting press B button to go back.
Go to Load Core again and choose "mame2016_libretro.so".
Take a look at the botton right of your screen. You will see "1.7.7 - MAME 2016 0.174".
This means the MAME 2016 (0.174) core is loaded and ready to be used in your Retroarch.
Now to launch a game with the MAME 2016 0.174 core, go to Load Content in the same menu > Start directory.
Then browse your Mame's roms path to "/userdata/roms/mame" and choose the rom filename you want play.
Eachtime a game required the MAME 2016 0.174 core, you have to start any game, manually load the core and start the good rom via the Retroarch's menu.
Retroarch provides MAME 2003 (0.78), MAME 2015 (0.160) cores as online update too.
I'm sorry if this mission is only for John Rambo, but it's the only bypass method I found for now.