Hi There,
Smart tags using Sensei has two options:
1. Untrained/Default smart tags: These are assigned to assets uploaded without any inputs from the user. How the Sensei trains is completely black-box and user does not have any control over it. I don't think once you remove any smart tags, that information ever goes out back to Sensei to correct the tags. Also this makes a bit of sense as personalizing tags can conflict with other users' way of tagging the same set of object. So no training to the best of my knowledge ever happens with any user action on DAM asset.
2. Enhanced smart tags: Here DAM users have a chance to personalize the tagging according to the context/usage/industry etc. Here also personalization happens for the instance only and it would not be shared with other AEM instance globally because of the reason of very personalized handling that user seems fit.
So in all Sensei does not seem to be affected by what individual users do with the tags that get assigned and I think it makes sense.
Thanks!