I can’t say when it will be possible to have two different chord symbols at the same rhythmic position, but you should be able to achieve what you need to by creating a chord symbol at the next rhythmic position, e.g. by setting the rhythmic grid to something small like 16th (semiquaver), then hitting creating a chord symbol one 16th after the position where the original chord symbol is found. You can then hide the new chord symbol on the staff or staves on which it should not appear, hide the original chord symbol on the staff or staves on which it should not appear, and nudge the new one into position in Engrave mode.