That's a lovely thing to say, but if your existence is being threatened by an aggressor, I wouldn't blame you for throwing out the rulebook.

In my view, if someone invades your territory and starts attacking you, you have no obligation to follow any sort of "principles" or "rules" when it comes to how you fight back. Anything you need to do to the attackers in order to defend yourself and your people is, by definition, morally defensible.

(Do note that I said "need". Doing arbitrary messed-up things that don't actually further the goal of driving back the attackers is not ok.)

FWIW, during the Iran-Iraq war (where Iraq invaded Iran), Iran used a bunch of pretty questionable tactics like suicide squads of child soldiers.