What are the characteristics of karmaless action? Assuming one has to operate in the temporal sphere, but seeks to diminish the karmic implications of action, what are the characteristics of karmaless actions?

Is this distinct from right action?
What are the characteristics of karmaless action?

It leads to dispassion.

Meaning, it's an action that reduces both karmic as well as mental / emotional entanglement.

Normal pathological action leads to entanglement in issues and trouble. Typical example is a child of a dysfunctional family, who is forced to inherit the bad circumstances and negative inertia, and by reacting destructively keeps creating causes for future trouble. Normal success-oriented action leads to positive entanglement in worldly affairs. Such as, when you are realizing yourself as a successful professional in any field.

Supramundane action leads to dispassion, to disentanglement, to letting go, to unbinding. How? Through counteracting/taming the forces of desire, aversion, and confusion.

So every time you act (whether directly or indirectly) towards reduction of desire, reduction of aversion, increase of wisdom - that's the supramundane action.

You can act towards reduction of desire and aversion by directly suppressing them and letting go - and realize wisdom as you practice this ("samatha followed by vipassana" in the broad sense). Or you can pursue wisdom and realize reduction of desire and aversion, and eventual dispassion - as a product of wisdom ("vipassana followed by samatha" metaphorically speaking). This is a theoretical construct meant to made the point. In practice everyone has to do both, in a spiral fashion - emotional intelligence and wisdom developing in lockstep.

While "karmaless" action can be ensured in the most straightforward way by literally leaving the world and engaging in practice of meditation (an approach typical of Theravada), a more effective approach, IMHO, is the Mahayana practice of not letting your ego indulge in self-sustaining activities. In other words, you should only do what leads to objectively optimal result (within the limits of your practical ability to achieve the optimum in the midst of a real life situation) and never let your social image, your ego, your group/tribe ego, your fears, your pride, (including your spiritual pride!), your bias etc. to get a bite of nutrition. This way all of your action will go towards dispassion and wisdom, as it will not be motivated by an egoistic motive (aka "passion").

Now, for the wisdom leg, this wisdom is not the worldly wisdom either. It is the special wisdom of understanding the nature of phenomena and mind, the nature of reality so to speak. So any action toward pursuit of this wisdom counts as "karmaless" action (action that leads to the ending of karma).

One notable characteristic of special wisdom is abandonment of overgeneralization and stereotyping. This leads to action that itself is not based on overgeneralization, stereotyping, and passionate side-taking - and encourages others to avoid overgeneralization, stereotyping, and passionate side-taking. Enlightened/enlightening action is inherently peaceful and brings peace.