@VeronicaSarver - Both ArcGIS Online and ArcGIS Enterprise have the same limitation of 200 unique values. One workaround is to apply the symbology in ArcGIS Pro (where there is no limitation) and publish as a web feature layer, as described in this Esri Support KB article. I would advise you to publish the new service as a test first before swapping out any services in the solution. I'm not sure of the implications of swapping the service without testing it.
For Roads and Highways, signs are treated as event features. You can add fields to the Signs feature layer that comes with the solution that would be recognized by R+H (RouteID, Measure, Event ID, FromDate, ToDate, LocError, and Offset), and feed the data into R+H using the Append Events geoprocessing tool.
Alternatively, you can use GP tools or Arcade to calc the fields that are recognized by R+H.