something like this?
How did I come up with this answer?
- When to Google.com (any other search engine would work).
- Searched for "adobe illustrator customize arrowhead". The less and more precise the terms, the better.
- Scanned down the list of results and noticed one of the links was from adobe.com. Clicked on it because, if the answer is in adobe's help files, then there is no point in searching around anymore.