I noticed that even though there are creatures that are normally small and unrideable on the island, available in the choosing Dino option menu, there is still a slight inconvience within the custom dino mode where players are still restricted to playing as Thee large and medium sized forcetamed stock creatures which are rideable, yet the other stock creatures which are the opposite still remain unrideable unless they are chosen from the menu or awaited until the modder adds them.

So I just thought up a suggestion for an add-on that may make not only the small and unrideable vanilla creatures rideable, but also the unrideable mod creatures as well. I was thinking maybe a easily craftable or spawnabld invisible mini-saddle that when applied to the small creature will forcefully equip them with the "Ride" option and at the same time shrink the rider (both visible or invisible) to the right size to mount them :)

Or maybe possibly even better, add a new console command that is something like "cheat makedinorideable" that will automatically give the player a chance to ride or become the creature they have tamed when facing them. But that would be optional since I'm not sure if something similar has been done yet ^^;