Set aside for a minute that you buddy sounds like a jerk, your buddy is also very wrong.
There are many hunting-related land access issues that are legally tricky (adverse possession, constructive easement, corner crossing), but this is not one of them. The legal answer is 100% clear. Your buddy's rationalization is mixing two separate issues, permission to take an animal of the state, and permission to be present on someone else's land. To legally take game on private land you need BOTH, but neither trumps the other. If his failed analysis was correct (that a game tag trumped private property rights), he wouldn't have needed landowner permission in the first place (limited or otherwise).
Legally the answer is very straight forward. If a private land owner grants you limited permission to be on his/her land, the minute you violate any one of those limitations you cease to have permission to be on the land and you are a trespasser, subject to all the penalties associated with that violation. Acting outside of the granted permission is essentially the same as never having permission in the first place.
I don't think that's right, and I would have to see case law to support your claim here. Land owners can NOT grant access to anything but their property. You're not asking for the right to shoot a deer, antelope, duck, or whatever...you're asking for access to the property. Landowners don't "own" wildlife, that's held in trust by the State and as such cant tell you what wildlife you can or can not shoot. The only authority that can set bag limits, seasons, method of take, etc. etc. is the GF Commission or State Legislature. A landowner can have RULES, but that's wayyyy different than Statute and Regulation.
What statute would be written, for a person that has trespassing permission, shooting a legal animal they have a license for? They have permission to hunt the land, they have a tag, they took the animal legally...what's the offense?
NO question it would be an a-hole move to shoot, say a bull elk when the land owner asked you to shoot only a cow...but about the worse thing that would happen would never being allowed access via trespassing permission or the landowner completely shutting access off for everyone.
I had a conversation some years ago with a Wyoming Game warden regarding a landowner that was charging "trophy fees" if you shot a certain sized antelope or buck deer. He flat told me, "if you hunt there and he asks for the trophy fee...tell him to pound sand, you have permission to the property and that's all you need."
Another interesting question, what if you have permission to access private property in checkerboard ownership, and the owner only wants you to shoot doe/cows and you find a bull/buck on State or Federal Land within the boundary of their private? Can you be fined for shooting a State owned animal on public land in that case?
I say no to both...there is no hunting violation.