Changing "When" an Instrument Change Takes Effect

I have two oboes in a score, one doubling on English Horn. The English horn begins the movement and then changes to Oboe. However, because the player doesn’t switch for about 16-20 bars, I get multiple systems of two blank Oboe staves, rather than having them condensed. Is there a way to change “when” the instrument change takes effect to eliminate this? It happens 5 or 6 times in my piece.

Unfortunately there isn’t a way of controlling where an instrument change takes place currently, other than to add something that prevents an instrument change to the part you want to “stay on”. One such item is a chord symbol region. However, it will also break multi-bar rests but you might be able to find a way of having it so that that still works? It depends on the music going on at various stages.