Hi Aurelien,
The map that is displayed comes from Google, so I don’t believe that they allow any modification of their icons. We are working on developing a Filter Bar though that could allow for filtering what is displayed on the map. Not exactly what you’ve described though.
As far as links to external booking websites, that is something that should be no problem at all. It could easily be added in the event description. And there’s a specific spot to add a weblink for the event, so that seems a likely candidate too.
Does that answer your questions?
— Julie