No need to edit files.
Key bindings for guns, bombs and rockets are right there in the Aircraft controls list
Make sure that you have the Keys tab selected (not the Axes one), then scroll down some... dunno, maybe 20% of the list.
What you're looking for is in the 4th or 5th sub-section, just after the Autopilot keys. Look for these lines:
Fire Guns (Machine Guns)
Fire Guns (Cannons)
...etc
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