How do you manage tags of imported sketchup models into another sketchup model?
If you need to keep your tag structure without adding anything:
Open the model you want to import in a blank file.
Inspect it and make sure it is what you want / need.
Delete all tags, move everything to ‘untagged’
Purge the model, save it, import it into your working model - or copy paste into your working model.
In your current model assign things as needed to existing tags.