NonCredibleDefense

By the same logic I would think this idea would be legal as well.

That's a thought, though I'd also point out that this might involve international law, and there might be different doctrines involved in international law.

Also, international law on involvement in warfare is fluid. I remember reading an article pointing out that if you go back, to, say, the pre-World War era, the obligations on non-involved parties were generally held to be much stricter -- like, doing something like having preferential arms export policy to one party would be considered involvement in a conflict. When Switzerland, earlier, refused to export Gepard ammunition to Ukraine, that's not really in line with the present norm, where countries often do provide arms to countries and consider that to be separate from being directly involved, but it does conform to historical rules on neutrality.

kagis

Not the article I was thinking of, but this is some related discussion:

https://crsreports.congress.gov/product/pdf/LSB/LSB10735/3

International neutrality law governs the legal relationship between countries that are not taking part in an international armed conflict (neutral states) and those that are engaged in such a conflict (belligerents). The international community developed the principles of the international law of neutrality in an era before the Charter of the United Nations (U.N.) prohibited using force as a tool to resolve international conflict. Scholars have described the law of neutrality as an “old body of law” with a “slightly musty quality” that does not always translate to modern warfare.

Russia and Ukraine are engaged in an international armed conflict and, thus, are belligerents. Under traditional conceptions of neutrality, sending “war material of any kind” to Ukraine or any other belligerent would violate a duty of neutrality; however, some countries, including the United States, have adopted the doctrine of qualified neutrality. Under this doctrine, states can take non-neutral acts when supporting the victim of an unlawful war of aggression. For the reasons discussed in an earlier Sidebar, Ukraine has firm grounds to contend that it is such a victim and is acting in self-defense. Under these circumstances, arms assistance to Ukraine would generally be lawful under the qualified neutrality doctrine, provided that Ukraine complies with other legal frameworks governing the conduct of hostilities.