Is it not possible to delete parameters from a widget once they have been added?

Yep. They can be removed from the widget source code. Either open from the source code button in Idea Studio, or the widget *.SRC in the directory. Remove all references to that parameter and delete the declaration line. Save the file, then import application changes and recompile.

Would like for this to be doable in Idea Studio though.

I've talked with support about this and they didn't put it in the designer because things tend to get nasty if you leave any references in.

Yeah, definitely would be nice if they could make this process easier. Not very user friendly. I had no issue figuring it out, thanks to Michaels post and it helps to have some coding experience so the source code didn't rack my brain. Less experienced users might have problems, especially since it seems like the stock widgets are very limited and any decent application will require custom widgets to do pretty basic displays/controls.

I would think they could make it so the delete function only works if after scanning the source code, it does not find any references to the parameter you wish to delete. That would force the user to go through each element of the widget and make sure that parameter is not used anywhere.

Then the other part of it would be updating any uses of that widget in the application. I had noticed that in the properties for the widget where you can assign tags/values/etc to the parameters the assignments can get royally screwed up (that might have been before importing the changes).