Well, since multi-turns has no strict turn order, that's somewhat impossible to do reliably. While you (as you probably know) can change the combatant's turn value, which changes it's position in the turn order, how it develops from there is up to all combatants that are part of the battle.
One possibility would be to have the skill impact your turn order calculation formula, e.g. the skill adding a status effect to the target, the formula could check for the effect (Check Status node) and e.g. simply return 0, i.e. their turn order doesn't change.
The only issue here is that a turn depending effect would never run out if the combatant doesn't have a turn. That would need to be handled via game events, e.g. using turn start events (on all combatants), where the event would:
- get all combatants in battle (e.g. Search Combatants node)
- use Change Effect Duration node to reduce the duration (i.e. -1 turn)
I don't think this'd impact the turn order preview, though.