Don't.
Remember our layer system is the result of lots of work on lots of simultaneous problems. As such, it is hard to improve but easy to break. Trust me. Further, layer management is far and away the most unpleasant standards task in the whole operation. You don't want to get involved.
OK, sometimes you have to. Maybe you really need a new layer. Maybe I told you you need one. If you're going to do it, you'd better do it right.
We're going to make the new F Trim Crown layer. Bring the layer dialog up.
The subject. Beta testers claim that GS actually floated worse ideas for the AC8 layer dialog. By the end of this exercise, you won't believe it.
(I'm showing the box short to save space. In real life, it's usually better to stretch it far as you can.)
Note: LC=layer combination.
1. On the left, highlight an LC in which the layer should be showing and unlocked. For the crown layer, that's any LC where the other 'F Trim' layers are showing and unlocked.
Explanation (Important): When a layer is created, it will be showing and unlocked in the selected LC, if any, assuming you remember to click 'Update'. In all the other LCs, it will be hidden (excellent) and unlocked (rats).
2. Click 'New'. Not that one, the other one. Upper right. Put in 'F Trim Crown.N'. 'N' is the extension. There should not be a space before the dot.
3. On the LC side, click 'Update'. Important: You must click 'Update' to modify LCs. Changing layers and clicking OK doesn't do it.
4. Make the layer show in all the LCs it needs to. That's all the LCs where trim is showing, plus the RCPs. Highlight the layer on the right. Select the first needed LC on the left. Scroll back so you can see the layer if necessary. Click the eye open. Click 'Update'. Click the next LC, scroll, click the eye, click 'Update'. Repeat until all the LCs are done, or your arm falls off. For output LCs, click the lock too.
The triangle. Bermuda would be proud.
5. You should also lock the layer in all the LCs where it is hidden, but I won't twist your arm. You can think of me maintaining the templates, though, as perfection is the goal with them. (Locked layers do not show in the palettes, a big feature.)
6. When you're done, OK the box and SAVE.
See also:
Creating Layer Combinations