To modify GUI items without going into the screen editor you can use the following API commands.
scr.SetProperty('ControlName', 'PropertyName', 'Value')
ControlName is the name of the control as seen in the screen editor tree
PropertyName can be any of the properties you see in the properties table in the screen editor
Value is just the value to change it to.
These 3 things must be entered as strings.
For example, to change the name of a button:
scr.SetProperty('btnZeroX', 'Label', 'ZeroX').
There is also the scr.GetProperty which you can use to retrieve properties from controls e.g. text from labels.
Regarding using 'Enter' to execute the MDI, you could set up a label and use the 'On Modify Script' to read the text entered and then execute it. But the 'On Modify Script' also runs when focus is lost from the label so may not always behave correctly.
Embedding the tool table into Mach4 hobby may be possible using wxwidgets but would be a lot of work unless you're already familiar with it. You can set a screen button to display the tool table rather than going through View>Tool Table if that is any better.
Hope this helps