Is there a option to untrim a solid?
If you mean you had a solid (any solid) and you cut a portion off of it using BooleanDifference or Split, then no. A lot of the information that is needed to reconstruct the original shape is gone forever.
The options for this are Untrim and ReplaceEdge. Usually, you need to explode the solid before you can use those tools (with some important exceptions.)
Also you can remove windows by using _DeleteHole.