I recently made a new? conventional defense to 1NT, and was wondering if asking for opinions on it would fit the site.
Questions about specifics are probably on topic, sometimes. Questions about "improving" it, though, aren't; too broad and too opinion based.
I want to play the convention that you lead T from KJT but J from JT against NT, to make it clear which I have. Is this a good idea?
No, it's not on topic. "Is this a good idea" is an opinion, and too broad. But...
I want to play the convention that you lead T from KJT but J from JT against NT, to make it clear which I have. What kind of issues would this result in?
That's more on topic. It might still be too broad if the thing you're asking about is broad, but the example here is at least reasonable.
Why is the standard to lead the J from KJT against notrump?
Yes, that's on topic. It's specific, it's asking why something is the default; while it's likely to also get a lot of "well, actually" answers, it should be reasonably answerable.
What is the standard lead from KJT against notrump? Why?
Yes, also on topic - similar to the prior question, it's nice and tidy. "Standard" might vary some, but it's still reasonably limited.
Here is my convention. Will this work? [2 pages of dense text]
Obviously, not on topic. Too broad.
So - I think the answer is, you can ask about particular things and why they're that way; and you probably could ask about a specific thing, but only if you were pretty specific, and perhaps asked about the standard way as a comparison.