Might be doable, or might be not.
Changing picture quality property to RAW+S3 appears to work in QEMU; no ERR70. However, you will no longer be able to change this setting from Canon menu (not even without ML). You will need YAMLMO to be able to switch back to the old state.
This setting is - unfortunately - camera-specific. Values valid on one camera may give ERR70 in another camera. That error will be persistent, even after removing the card. It's recoverable (with manual intervention), but I prefer to avoid this.
Even if you don't get ERR70, pictures saved at this setting may or may not be valid (or the camera may crash). In the past, we've got many problems with hacks like this, so I prefer to avoid them.
I might expose this setting to Lua at some point, but
only with a whitelist of known working configurations, and
only after checking every single setting in QEMU.
Related:
https://www.magiclantern.fm/forum/index.php?topic=20101.0https://bitbucket.org/hudson/magic-lantern/pull-requests/753/bad-settings-warning/diff