Any advice on how to remove (to replace) the downhaul on my NP mast extension?
I have undone the only two screws I can find but can't remove anything.
I can't figure it out ....????? And my next step would typically be to inadvertently break something...which I am trying to avoid
It's Np , which means it's unnecessary complicated and will jam up with sand even if there is no sand .
Look down those slots , could be a knot end that you will need a very fine needle nose pliers to pull out . Or a fine hooky thing and a lot of swearing . The one I had was similar but different .
If you do figure it out , don't loose the tiny brass sleeve that presses up to the knot so it won't cut the rope on the sharp inside of the pulley casting.
ps , I use NP sails but will never again use NP extensions. Horrid. In the vid it looks soo easy whipping the rope around those bottom pulleys , in reality it's easier threading through a hole , ( like you do with the sail pulleys ) , .Any loss of concentration , ( which is me all over ) , and the rope jumps all over the place like a mad woman's sh.t.
Chinook 
Is that an MXT with a Europin adapter, or is that the way the extension comes?
Edit:You made me check my extensions, and what i think you have there is an MXT with the Europin adapter installed. I have no idea how that is removed, but you need to remove it. The rope end is directly inline with the axis of those pulleys. I suspect that on the bottom you need to slide that lever thing in order to get the Euro adapter out.
A different type of MXT extension, at least in the RDM size, has the cleat facing the other way, but the rope end knot is accessible from the top and is really obvious. You don't have that type. The knot for yours is on the inside of the mast tube bit, under that adapter.
Select to expand quoteImax1 said..
... I use NP sails but will never again use NP extensions. Horrid. In the vid it looks soo easy whipping the rope around those bottom pulleys , in reality it's easier threading through a hole , ( like you do with the sail pulleys ) , .Any loss of concentration , ( which is me all over ) , and the rope jumps all over the place like a mad woman's sh.t.
Chinook
I love the MXT extensions. At least the ones that they had where the cleat aligned with my downhaul whinch. The next series seemed to have gone in a different direction, which just sucks. But the pulleys are still good.
Are you sure you are not threading the pulleys on the sail incorrectly?
Select to expand quotecs66 said..
Any advice on how to remove (to replace) the downhaul on my NP mast extension?
I have undone the only two screws I can find but can't remove anything.
I can't figure it out ....????? And my next step would typically be to inadvertently break something...which I am trying to avoid
I'm guessing you bought this secondhand and didn't realise the previous owner has fitted an MXT to UXT adaptor. An MXT to UXT adaptor allows you to convert your MXT extension to a UXT so you can euro/north pin deck plate.
To change the rope, you need to remove the adaptor, I "think" you push the release button and pull out the adaptor at the same time (might be a bit stubborn so use brut force). Then you will see the knot at the end of the rope. Like a lot of extensions, it'll probably be properly wedged/jammed in tight, so just cut the rope on the pulley side and use a nail to push the rope through.
Its worth using a double knot when replacing as its less likely to jam in future.
I hope this helps mate.
Many thanks for your helpful replies, it seems it is a UXT adapter as described above (I had no idea), now at least I know which part I have to fight with to remove 
