What is meant by "make sacrifice of a corpse"?

Anything can be sacrificed — the modern trope of live sacrifice as being the inherent meaning of “sacrifice” is an unfortunately lurid distortion. (I blame pulp fiction and TV's reliance on bloody sacrifice as a shorthand for “these are bad people”, but I have no cite for that.)

Most online dictionaries limit themselves to the “kill an animal” meaning, but the Merriam online dictionary is more expansive, and even shows the distinction between the meaning that conflates sacrifice with killing and the meaning that doesn't, by including in its fuller definition two senses that are nearly identical except for that conflation:

sacrifice
noun
1 : an act of offering to a deity something precious; especially : the killing of a victim on an altar
2 : something offered in sacrifice

Both senses are primarily the broader meaning of religious sacrifice as an offering of anything. Despite the semantic narrowing to just sacrificial killing that the word is undergoing in modern English use, reflected in sense (1) above, sacrifice can still be correctly and meaningfully applied to something already dead.

When that misunderstanding is dispensed with, it's easy to understand what “make sacrifice of a corpse” means.

The specifics of how a corpse could be made a sacrifice depend inherently on the rites of (real or fictious) religions of the world in question — the most familiar real-world method to the English-speaking world is to burn the sacrifice, in the sense of the biblical “burnt offering.” Other sacrificial rituals may not involve destruction of the offering at all, and may be only symbolic (which in a fantasy setting, can easily be magically/metaphysically real beyond “only” symbolism). In a fantasy setting, such rites could be quite different from modern Western assumptions of what “a religious sacrifice” looks like, limited only by the imagination of the setting's author(s).

To observe this prohibition, then, a follower of the fictitious god Tyr would have to avoid participating in any rites of other in-setting religions that involve sacrificing a corpse.

In other RPG games (like ADOM, for example) one can pick up corpses and drop them on an altar of a deity as a sacrifice. The sacrifice does not have to be a live one. It can be an artifact, gold, or a corpse.

It seems in the RPG you're describing never sacrificing a corpse is part of showing respect for fallen enemies. Their corpses must not be sacrificed.

It's just an educated guess on my part, as I've never played the game. Hope it helps.

As many WOTC rulebooks tend to be, this phrase is poorly written and evokes numerous interpretations of what this means.

To me, "make sacrifice of corpses" sounds like defiling enemy corpses in the name of Tyr. For example, blessing these kills in the name of Tyr or something after killing them could be considered disrespectful in the eyes of whatever god they worship.

The whole statement seems to read "treat fallen enemies as you would fallen comrades".

In the Viking religion, (which I'm guessing from the name Tyr is the basis here) you could sacrifice by dedicating to a particular god anything valuable, which certainly included enemies (either their war-gear or the reputation you gained by killing them). How this was supposed to work is not clear at this distance, but there is a record in the sagas of a hero sacrificing an enemy army in advance by hurling a spear over it and shouting "Odin has you!" (apparently the sacrifice was accepted; certainly the battle was won).