Does anyone else know about this trick where you can make the basher create a hill for the Lemmings to walk up inside a terrain? Here's an example of what I'm talking:
All you have is builder and Basher, while having no Blocker to turn them around.

Now this is how it looks when you finished it:

You can turn the terrains into stairs by stopping the Basher at a certain time. I once made a level like this in the PSP Lemmings where this trick is needed to get pass the big terrains full of logs:
Yeah, that's a fairly well-known trick, not sure how often it's been featured in custom levels though.
The
challenge board on this forum probably has a number of usages of this trick scattered throughout as well. The latest example of its use can be seen in certain challenge solutions for Beach 7 in Lemmings 2 for PC. Here's a
screenshot of it in action (plus other unrelated things, but you should be able to tell the parts where a basher was interrupted mid-stroke, in that level using jumpers instead of builders). [note: download URL requires log-in to forum to work]
And it looks like from your screenshots that you've gotten the hang of level editing with LemEdit and CustLemm.

Hope to see some fun and interesting levels soon!
Wow people already knew about this?

I actually thought I discovered it.
We're talking about a game that has been out since 1991, been ported to just about every computer and console system in existence, and been played by millions of people. Your chances of being the first person to have discovered something about the game is not high I'm afraid.
Danger 28 of my Lemmings Plus pack relies on that trick, and as has been said, many challenge solutions rely on it.