How can I create my own slide layout that appears in the pane?

[Guest]

I've created a series of slides that all have the same modified slide layout
- Can I save that layout so that it appears in the layout pane when I create
a new slide? Ideally, I'd like it to be a slide master, but it appears you
can't add new placeholders on a master and the layout I'm using has 3 text
placeholders. Also, can I limit what appears on the slide layout so when I
create new presentations based off this one, I only see the slide layout I
created?

 

[Guest]

The new master won't appear in the slide layout pane, but it will appear in
the slide design task pane in the "used in this presentation" area.