Insert a Code component in Builder and try something like this in the Begin routine
tab:
win.mouseVisible = True
and in the End routine
tab:
win.mouseVisible = False
Generally, no. A code component in Builder allows you to execute small amounts of code at relevant times, while still staying within the graphical Builder environment.
Yes, there is no way to translate the arbitrary Python code you could write and turn it back into a graphical representation. So going from Builder to Coder is very much a one-way street.
But you will likely find that using a code component within Builder allows you to achieve 99% of what you might need to do with custom code, and actually stops a lot of errors by automatically inserting the code at the right place. i.e. you get to have your cake and eat it, by using custom code but remaining within the Builder environment.