I don't think that is true at all.Not if I just keep it normal tip, either no foot or the original hard rubber foot grinding down thin. The one with spike is out already.
If you hit someone with your cane, with or without a spike, with or without modifications, or with that silly ring you bought, or stab them with a knife, or shoot them, it is all the same in the eyes of the law. It doesn't matter what weapon you used, all that matters is "was using a weapon justified".
If it wasn't, you're in trouble. If it was, you're not.