Will a 2/0 aluminum conductor be allowed from a 100 amp. main disconnect provided by power company on a pole to a 125 amp. load center, main panel in the building ?
What is your rule in your area on how to treat the disconnect provided by POCO? Is it considered service disconnect or not?
Either way your 2/0 Al is more than 125 amp ampacity though, so it mostly comes down to whether there is large enough lugs or enough wire bending space on either end.