Tooled Leather definition:
What is tooled leather? It’s actually very simple, it’s any piece of leather that has been worked on in any way to have a design, initials, pattern or other decorative look applied to it.
You use leather tools to make any decorative designs or patterns in leather. So tooled leather, means a piece of leather that has been tooled, or worked on, to make a design on it.


As mentioned above, Brooks most likely used a large die to cut and emboss (tool) the leather at the same time. Almost all of the mass produced saddles would have it done this way to reduce costs much like the "custom" (not really) boots and belts that we still see today.
One off's, meaning those that are not production embossed can be quite expensive because they are labor intensive...even if the same pattern is attempted there will be slight differences because of the hand work etc....compare the differences in CWD, Devoucoux, Hermes saddles with the mass produced "tooled" ones and the difference is quite apparent.
If you are planning to do some simple tooling on an existing bicycle saddle, depending on the level of intricacy you might want to start off with a simple design.
Tandy makes a range of embossing tools that you could use to "customize" you saddle....of course, you will need to place a block on the opposite side of the piece you are working on to get a clean stamp and reduce rebound and double stamp...if you are using swivel cutting tools, that's another matter.
If you are really interested in doing it yourself I would suggest googling leather tooling to get a primer...too much info that can't be relayed here. There will also be information on antiquing.
Good Luck, Ben