I wish to change the silver mine building chain on Sardinia into a town building chain.

I went into the startpos to find it's called "silver:sardinia:iglesias"

Then I went into the main pack into db files and then into "campaign_map_slots" and found out that silver:sardinia:iglesias had the building chain "silver". I changed that into being "town" instead.

But when I opened up the campaign, nothing was changed. Even when I destroyed the existing silver mine. I've tried this but with changing it to a farm and iron mine but nothing works.

(Note that I don't simply want to change the building, but the entire chain. So if I destroy the building it should be a new chain)

... How do I do it?