Was Napoleon the first person to seriously contemplate territorial aggrandizement at the expense of Venice? It seems like they're pretty moribund and there's a ton of land up for the taking there, either for Felipe or in exchange for more land for him. Would it just upset the balance of power too much?
He was not, Austria looked at some Venetian lands greedily.
However, legalities. Anyone wanting Venetian territory would have needed some sort of justification that, at this point, utterly lacked (Venice was neutral in most wars of the period, except when fighting the Ottomans, usually in alliance with Austria). An unprovoked attack against a small power with aims of naked territorial aggrandizement was, generally speaking, NOT quite within the rules of European diplomacy of the period, however messy they were.
You needed something resembling a valid claim or excuse. If not, other powers would have reacted in order to keep the balance of power, and even with a perfectly valid claim, foreign intervention was not impossible.
Of course, in this era, Venetian ability to protect mainland holdings alone was minimal. They were still a decently sized naval power.