Haven't tried any scenario's yet, but with blueprints the game asks whether you want to overwrite the existing design. Afterwards it can be uploaded via content manager and the old design gets updated.
I don't know if the difference in names is what causes your issue.

I was looking for information about this and couldn't really find anything else except this thread.
It seems like it work as follows:

Ride must be edited and replaced in the same save as the original version of the ride. It needs to be the ride from the save that created the original blueprint. Otherwise it will upload a new mod to the workshop and not just replacing the old one.
You cannot start a new save and place your blueprint down and edit that with the hope of updating your mod, because it will only give you the ability to 'share' it instead of updating the old one. A bit wonky but that's how it seem to work.

When it comes to scenarios I don't know exactly how it'll work but I suppose you need to have the original save file for it to be able to update the old scenario mod.