In case there are any changes that need to be made in the policy such as address change or any particular changes regarding the automobile or its usage, it could be done by an endorsement by the insurance provider. You need to submit a letter to your insurance provider along with the proof of the changes so that you could obtain the endorsement. There are few endorsements that might charge an extra premium from you.
There are many factors such as IDV, deductibles, seating capacity, cubic capacity, previous insurance history etc. that affect the insurance premium that you would pay. For comprehensive insurance plans, premium charges vary insurance provider per insurance provider on the basis of the coverage provided. Compare insurance premiums so that you get the best quote.