In the OTL Roman Empire,the Germanic people were considered as Barbarians and they didn't have a good treatment or reputation inside the Empire. This is evident by the treatment of Alaric,Merobaudes and Stillicho along with other Gothic settlers inside the Empire.
In an ATL,I would want you to have one or more Germanic peoples considered as Non Barbarian like the Galatians,Gauls who joined the Empire,Greeks,Anatolians like Zeno(emperor of the East in 476),etc. You can have your choice if you want them West Germanic like Franks or Saxons or North Germanic like Vandals(?),Norse,Danes or Swedes or East Germanic like Goths or one from all. You can have ways to obtain citizenship in Rome by serving/building up something and then getting freed or a large number of well treated Germanic origin Slaves who get freed after good service and consider themselves Roman or even joining in like the Galatians and the Gauls or something like that. How would this affect the later Roman Empire which could be led by a Germanic dynasty and what effects would that have on the Germanic states that appeared after Rome and so on?