We know that a lot of Nords settled at various times of history into High Rock. They even built their own settlements, of which even the capital of High Rock, Daggerfall was originally a Nord settlement.

I am lead to believe that these Nord families habe become absorbed into Breton society, but I am curious as to whether these families hang onto or maintain anything from their Nordic roots?

One example we see is Hjalti Early-beard who was born to a family in High Rock. By his name we can see that it is obviously a Nord family name by both the Christian name as Hjalti in real-world is a Norse name most famous for being the name of an Icelandic King, and also the surname being a descriptive & double-barrelled. This would mean that the Hjalti's family could have recently moved to High Rock or they could have been descendants of earlier Nordic settlements.

Is there anything in lore that speaks of High Rock Nords and whether there is noticeable differences between them and the magical Bretons of mixed Nedic & Elven roots?

I wager that aside from you're stock Nords that may have recently moved to High ROck/somehow managed to hold off having children with any other race, I figure like the majority of High Rock they also would have a mixed heritage as well. You might have places where Nordic traditions are intact, if not slightly warped, its possible that they would be more Bretonic then Nordic. Places like Alcaire might have a strong Nordic influence to it, High Rock is a giant hodge podge of cultures and traditions mixing in at varying degrees. You might not be able to find universal similarities between the Nords in High Rock. I figure knight culture would be popular in among Nords of High Rock though.