By 18th century usage, civilians incurred death penalty if taking arms against soldiers. Be the soldier a subject of the legitimate sovereign who occupied the region by legitimate divine right, or the citizen of the Republic who liberated the region of monarchy.
Which, interestingly, was precisely what the people of Paris had done.
Yes, those classed as partisans, guerilleros, francs tireurs, and other combatants captured out of uniform were regarded as having forfeited the customary rights of quarter and subject to summary execution, and continued to be so up until the end of the Nazi occupation of Europe. Civilians resisting, or insurgents rising up against an occupying army might be regarded as morally disinct although equally inconvenient and ended up being executed as well, with or without legal process.
I wonder how comforting it was for the Piedmontese nationalists to be executed by citizens of a republic liberating their country from monarchy whether or not that change was an outcome they had invited.