Yes, you can edit Gcode. It is text so any editor can conceivably open it but you may need Notepad++ or similar editor which has the ability to open insanely huge documents.
The first 600 lines of Bambu Gcode include a lot of preamble setup data. Although its been a while since I last looked at it, it has all of the setup parameters needed to get the printer ready to print. What you see on the slicer screen I I am not mistaken, is the Gcode for only that layer. This is for ease of use otherwise, you’d want to use an editor.
Having said all that, the Gcode in the slicer has been parsed for safety. If you go mucking around with it and don’t know what you’re doing, you could easily force the nozzle to an x,y,z coordinate that will damage your printer such as trying to force the nozzle below the build plate. That doesn’t mean you shouldn’t give it a try, just be careful and have your finger over the pause button on the printers control panel just in case. 
There are some pretty cool functionality that is documented in this post if you care to play around.