Ok i have a problem, it is thus:

Our map has many stairs, hundreds of stairs. But these are made from map instances, there are four stair objects and four instances of each, so 16 in total.

These stair objects have icon states defined in code, and this is good. The issue is oddly, they also have icon states defined as edited vars on the map instances, this is bad.

What i would like to do, is to remove this information from the map instances, so that those instances will just follow what the compiled code says for their icon states.

I can't seem to find any way to do that in the editor though, all i can do is change the state to what i've coded in. Which works well enough, but it means it won't be updated with future code changes.

Manually replacing all the stairs with newly created instances is not an option, there are too many
You should be able to Find/Replace the instances to something else.
If you mean about one type of object, just open your map file in notepad and change values you need.
Im not sure it will work, but just try.
Just remember to make backup!

As Kaio said, you can find/replace instances.

From the instance editor you can right-click an instance and select "Find instance on map".

In that dialog you'll notice that the 'Find' box is a number, not a type-path.

Next you put the base type of the object in the 'replace' input and hit "Replace All" -- rinse and repeat.

You can use "replace" alone a few times just to make sure you're not gonna break anything by replacing the instances one at a time until you're sure.

You can leave the "Replace" box empty to delete the objects.