Lapp Codicil of 1751 is an addendum to the Stromstad Treaty of 1751 that defined the Norwegian-Swedish border. It consists of 30 sections.
This special codicil formalised the rights of the Lapps or Sámi (Sami people) to continue with their traditional migratory reindeer herding across the newly formalised border between the then Danish territory of Norway and Sweden. It also had provisions about citizenship and taxes among other things.
The codicil has been considered to guarantee Sami rights in traditional Sami areas and is still considered of importance in the debate about these rights.
References
Lapp Codicil of 1751 Wikipedia(Text) CC BY-SA