I have a route idea and for the timetable would like 66 to layer in from the various packs. Is there a way to ensure only the EWS livery spawns, though? The DB, ONE and DRS liveries aren't appropriate.
That depends how those are configured region-wise. You can only specify minimum length, speed, power and regions. If the other 66 are from different regions, you could try to exclude them by being very specific about the allowed regions. But if other locos are compatible as well (not only 66), they could spawn in as well. There is no way to explicitly allow only particular locos.
