If anything's to be done here, it needs to be reopened as separate and more detailed issues, and it would be feature requests.

I tested a codename field and it didn't split up. It might if I used a dot in it. The fields aren't treated differently from others - it identifies words. So you might add a feature request to request codename fields do not be split up even if they look like multiple words.

All fields are used for keyword fields, regardless of visibility. I think it would be a wrong assumption that keywords should only be drawn from visible fields. A feature request might be considered to determine which fields are scanned for keywords.

Codenames being read only would also have to be a separate issue. It would need to be configurable, as it's perfectly normal that someone may want to change a codename. For example, a SKU may have been wrongly input, product codenames may have been changed, or all kinds of things.