Woe is me! The node is locked and I cannot add my writeup! The editors are cruel! Everyone hates me! The computer hates me! The editors hate me! The users hate me!
So you stumble across a node that has a note at the bottom saying something along the lines of
No more writeups are being accepted for this node.

What has happened is that some time before you graced the node with your browser clicks - someone (or several someones) made the mistake of causing a cascade of poorly done writeups. Often these writeups are at -10 or there abouts when the editors do get around to cleaning up the node. Frankly, they don't have enough time to constantly monitor all those nodes out there that teeter on the edge of GTKY oblivion causing even the good nodes in there to be killed.

Thus, the editors lock the nodes. This does not mean that it is the end of the world. There are several possibilities for you to express your ideas.

First off, message someone who already has an existing writeup there to include your ideas along side his or her own. This is by far the most suggested (even if the node isn't locked) if your own ideas are short in length.

Next, you can write your writeup in your scratch pad and ask an editor if you could add it to the locked node. If the node would add something new and wouldn't be downvoted to horrendously low reputations that would result in its immediate killing, most editors are quite willing to open up the node for the brief moment that it takes you to do this. On the day of the original writing I recall seeing a node cross the new writeups in a node that had been locked a week earlier.

And there you have the essence of the idea - this user took a week to write one node rather than just slapping it together. It was well done and formatted and clearly added new ideas.

Lastly, you can go find some other node that almost has your idea and add to it. Be wary though your writeup will still face the "is this a worthy writeup" test from your peers. If you write one that suggests to others to add their own lists no amount of hiding the writeup at time of creation will prevent everyone else from doing it - it just takes one bad writeup to catch the eye of an editor on a GTKY node to clean the entire thing up.

By far, I suggest asking an editor to glance over it and unlock the node. If it won't survive in that node, it is not likely to survive outside of it either. Take time to write it - as you would with any other node.