As this is an ancillary you need to edit the export_descr_ancillaries.txt. First find the crown of the faction you want to edit and remove the settlement requirement. For example for the English crown:
Code:
Trigger englishcrown
WhenToTest CharacterTurnEnd
Condition IsFactionLeader
and EndedInSettlement
and SettlementName London
and not FactionExcommunicated
and not HasAncType royal ;not already holding crown
and FactionType england
AcquireAncillary ccrown01 chance 100
You would need to remove the parts highlighted in red so you're left with this:
Code:
Trigger englishcrown
WhenToTest CharacterTurnEnd
Condition IsFactionLeader
and not FactionExcommunicated
and not HasAncType royal ;not already holding crown
and FactionType england
AcquireAncillary ccrown01 chance 100
Thus the faction leader will automatically get the crown.
To change the capital you need to change the 'and SettlementName' part to the name of the settlement where you're coronated.