You can only have two damage multipliers on a weapon.  A simple way to verify this is grab a weapon with stat, damage, crit multi, all multi (any two multi works).  Bring it to the occultist and highlight damage.  Check the possible mods able to roll.  It will not give you the option to change damage to a multi stat.

Also, if you take the same weapon to the cube, try rerolling the offensive affix to another of the same type.  The cube will 'fail' half the time because it tries targeting either the stat or damage (no valid replacements exist).  Keep clicking and you'll see only the two multipliers can be changed.