6d is quite fun, you need to think of a word for wife-swappers then replace two consecutive letters which stand for a women’s group with one half of ‘pose’.
I see now that the definition in 4 dn is "changes" so again I correct myself.
But I can't see why 10 ac is such a great clue. "Opposite of T-bone" doesn't tell me to drop the letter T.
10a - I chose this as my joint COD because of its clever use of disguising the fact that you need to deduct a T from a bone, as in 'bone - T', by the use of "opposite" followed by a popular cut off steak ie T-bone.
Sorry Jono, I see you answered this about 15 hours ago.
Honestly, I take so long to write some of my posts with constant tinkering that's it's a wonder they even appear on the same day as the question they're answering!
Thanks all for your explanations. When you see them you realise that, while tough, this is a good crossword. I don't mind slightly contrived, off the wall, parsing if the crossers give you a bit of a helping hand up front.