I could see Italy going with a
Praying Mantis-style vehicle built on top of one of their light tanks to try to keep the hulls useful as the war progresses.
Maybe add in the
Trombocino as a infantry platoon weapon.
Put the
Piaggio P.108A on anti-shipping duty with a 90mm cannon in the nose (one prototype built OTL)
Italy'd be a reasonable choice for a country developing cargo subs too, come to think of it, given their prewar expansion into Africa, specialist frogman program and fear of the Royal Navy.
Have them capture some
Pyrkal proto-assault rifles from the Greeks.
Mix in a dash of WW1-era weapons hastily reactivated when the war moves onto Italian soil- captured Austrian pneumatic mortars, the
Villar-Perosa, a variety of civilian shotguns getting issued out to frontline units.
There's a perfectly reasonable path to the Italians developing a rocket-propelled fighter, given their efforts to develop the Campini motor-jet, which were unlikely to be successful but reportedly involved designing an airframe and their desperate need for air defense by 1943. If you can't put a jet into your jet fighter airframe a rocket is the next best thing, after all.
Just keep the Red Devil grenade as is with no modifications. But have the Italian Army decide to copy some of the British Sticky Bombs they captured in North Africa.
Now, have the allies start shipping all these captured Italian weapons to support the Yugoslav Partisans, with their fondness for knives as a sidearm, brigade of M3 light tanks, and pre-existing reliance on a mish-mash of captured or smuggled in weapons from across the globe, including all the fun OSS and SOE liberator pistols and silenced Stens and so on. Then give the British
Raiding Support Regiment another battery (or just re-equip C Battery, their AA battery), this one equipped with rocket Z batteries for air defense, and remember that the reported genesis for the Land Mattress was a Z battery used in a ground role in North Africa and that Luftwaffe activity over Yugoslavia was declining rapidly by 1944.
Now, imagine being a Yugoslav Army officer trying to coordinate logistics in the last offensives in 1945, and despair.