Just a couple of notes:

[...] instead of refusing to abide by their treaty and ultimately switching over to the allies during the conflict?

This is incorrect. The Italian government did not abide to the treaty since it was a defensive agreement... meaning that its provision were unapplicable nevertheless due to Austria-Hungary having started the war in the first place.

Moreover, the A-H government had already refused multiple times to either hand those very same territories or make any concession whatsoever to its Italian ally; the worsening conditions of the ethnic Italians in the Empire, the sheer impopularity of the Treaty itself - let's not forget that Italy had fought three wars of Independence against the Austrians - which had been signed in 1882 by prime minister Francesco Crispi in spite of the French (they had seized Tunisia a year before without his government's consent...) was what led to Italy ultimately forsaking the agreement.

Moreover, this did not happen mid-conflict but sometime before Italy's entry into the war on May 24, 1915.

[...] Did Mussolini also feel the Italian government should have acted differently [...]

As it's already been explained no, not at all. The very fact of Italy joining the war against the Central Powers was largely justified from an Italian perspective, and Mussolini himself not only supported the war effort but also enlisted as a volunteer (even though he had more than happily evaded his duty to be conscripted in 1902).

[...] These territories were Trentino & South Tyrol, Dalmatia, Trieste and Fiume [...]

Actually these were Istria - which comprises both Trieste and Fiume - Dalmatia and Trentino. South Tyrol was added in a second moment not so much because of the (tiny) Italian minority there, but also because it provided a more easily defendable front-line; it was, in other words, a strategically convenient place.

'Italia irredentia'

For everybody's information, that'd be spelt "Italia irredenta".

The whole reason the Italians went to war was to annex 'Italia irredentia', those territories of the Austro-Hungarian Empire that were populated with Italians, but had not been conquered in the Italian Wars of Unification.

These territories were Trentino & South Tyrol, Dalmatia, Trieste and Fiume. Mussolini was nothing if not an Italian nationalist, and had welcomed Italy's entry into the war as a socialist. In the end, Italy DID get Trentino & South Tyrol, Trieste AND Fiume; unfortunately, only small parts of Dalmatia were handed over, since the bulk of the territory was populated with Croatians. This led the Italian delegation to walk out of the Treaty of Versailles, and gave rise to the 'Marred Victory' myth, that proved vital in the founding of Italian Fascism.

Sources: David Stevenson, "1914-1918" Margaret Macmillan, "Paris 1919"