API or Macro to reduce the Initiative Score when moved to the next in line?

We're trying a new counting system for our homebrew game where the counter goes down by 5 or 10 depending on the type of character once they go (so a 20 Initiative would go to 15 or 10). Is there an API or Macro that I can use to force that instead of trying to do it mid combat? Our DM prefers things to be as automated as possible so a quick button press would be nicer than pausing to change it manually.  Thanks.

Hi Laura I don't know about API scripts as am not Pro user, but I would use the Custom Item section.  I'd have everyone roll initiative to get their rolls entered in the tracker and then make a duplicate entry for each one (in the Item Label area)with the -5 or -10 in the line below (Round Calculation).  Add it to the tracker, change the initiative number to the score rolled and delete the original entry.  Not super speedy, but an easy thing to do and is only once per combat

From the wiki (<a href="https://wiki.roll20.net/Macros/Initiative" rel="nofollow">https://wiki.roll20.net/Macros/Initiative</a>): For a game such as Shadowrun where you want to subtract 10 from the current initiative after every turn, you could have a global macro like so: /em @{selected|token_name} ends their turn. [[10 &amp;{tracker:-}]] So you simply need to setup two macros that use the above command and you're all set: one to reduce initiative by 10 (the one given) and one to reduce initiative by 5.

Thank you so much Manny, that is exactly what I was looking for!