Yeah...not all directors will allow such tricks...but I think the tricks Daniel's talking about are not really ' playing' tricks...but more like flexibile re-arrangement and decisions taken by the conductor for efficiency.
I know that some conductors will change or split ( for instance ) double stoppings into a2( 2 groups ) and such... and having 1 section playing in 3rd positions and the other in the first just to en-rich the sound...
And most importantly... to take turns to hold long tied notes...the orchestra doesn't really hold the notes or rather diminuendo/crescendo at the same point of time to ensure a seamless flow, and sometimes for tonal effects.
But most apparently, and almost essentially so, is when the mute is employed in orchestral playing( esp. with the cellos). U can't have all the cellists stop playing to adjust the mute at one same point of time. So what they do, is taking turns...maybe four at a time and so on...
These flexible options really greatly facilitate playing.
But some ensembles believe in -absolutely-no-change- with regards to original arrangements and performance directions and so on.
I find that both parties are right. But if slight amendments will facilitate playing and make the session more enjoyable( ensemble playing at the advanced level can be more of a stressful thing than enjoyable)...Why not then?