Naval aircraft can and do operate from land bases all the time. This has always been the case.

Usually they fly from their land bases to their carriers when starting a deployment, and practice mostly from land bases (even carrier landings can be practiced there, with the outlines of carrier decks being painted on the runways for example).

The aircraft themselves need no modifications. Torpedo bombers (both Japanese, British, and American, as well as those of other powers that had them) almost universally doubled as regular level flight bombers. When doing level bombing missions they tended to fly higher, the main reason for the very low level flight on a torpedo run being the need to drop the torpedo from those low altitudes to prevent it hitting the water too hard (or at the wrong angle) and breaking up. With regular bombs you don't have that problem, unless you're doing crazy stuff like the dam busters raid (which was more akin to a torpedo run than regular bombing because of the nature of the special bombs used).

As hinted already, logistics might become a problem as parts commonality often is limited between navy and air force aircraft. But if the deployments are separated geographically (as the Japanese IJN did it) that's not so much of a problem as you'd just be docking your fleet supply ships near the air fields instead of doing underway replenishment of your carriers with them.

Of course if your navy aircraft are floatplanes rather than carrier planes, that limits their use to areas with large enough lakes or shorelines unless you want to go to the expense of converting them to have regular landing gear.

How hard would the technical problems be in real life?

None at all. Naval aircraft are already expected to operate off land bases, defend land targets, and attack them.

The Pacific War was almost entirely the responsibility of the Imperial Japanese Navy (IJN), the Imperial Japanese Army (IJA) was busy in China and had their own aircraft models. Most Japanese held island airbases were stocked with unmodified IJN aircraft. In the very late war, after the IJN fleet carriers had been sunk, some IJN aircraft were lightly modified to be optimized for use exclusively on land.

torpedo bombers would have to be retrofitted with high explosive bombs...

Japanese torpedo bombers already had the capability to drop bombs, so did everyone else, and were expected to attack ground targets and operate from land bases. Torpedo bombers, being large and able to carry heavy loads, were given many tasks. The Japanese B5N "Kate" torpedo bomber, and its successor the B6N "Jill" could carry a torpedo, various bomb loads, and depth charges. It could act as a torpedo bomber, or level bomber, or do anti-submarine work. Later models could carry radar to act as search and early warning pickets.

torpedo bombers' low flight levels might subject them to anti-aircraft fire

Torpedo bombers were already subjected to heavy AA fire as they flew very low, quite slow, and unnervingly steady to drop a torpedo against a ship. When used as bombers against land targets they had a much easier time being able to fly as high as they like.

Historical Examples

In 1938 the B5N participated in the Japanese war in China from both carriers and shore bases.

Half the torpedo bombers in the first wave at Pearl Harbor were armed with 800 kg armor piercing bombs to attack ships. The second wave was entirely bomb armed to attack hangers and grounded aircraft.

During the Battle of Midway, the Japanese used their B5N torpedo bombers as bombers to attack Midway island. Later, as the Japanese were preparing a follow up strike, US carriers appeared. They faced a dilemma: rearm their torpedo bombers with torpedoes or attack immediately with general purpose bombs. They decided to rearm with torpedoes. This delay cost them.

By late 1944 most of the IJN's fleet carriers were sunk. The remaining light carriers could not operate heavy torpedo bombers. Remaining B5Ns and B6N torpedo bombers were largely from land bases.