So if we become a 10B MC and we print 10% HDB. That would be 1B, if the price stays long enough on that level?

And if the price goes down again to 1B MC in that example we have 100% inflation if the HDB converted at this price to Hive?

No, because of the cap. HDB would be devalued down to 100M so the added inflation (if all converted, or if doing some sort of "mark to market" on unconverted HDB) would be 10% still.