Yes,you should be able to have a qualified gunsmith do the work for you.I would check out the area in which you live and find a qualified gunsmith perform the work for you.
Introduced in 1973, the Citori was the first Japanese made Browning. Fixed chokes were the only option until the Invector choke became available in 1983. The fixed chokes and Invectors were both available on the Citori for a few years until in 1989 when the Invector became standard on all guages except the 28ga and .410.
All Citoris were/are made in Japan, and that is not the full serial number. There are three more numbers and two letters. Value depends mainly on the features and condition. Early Citoris with fixed chokes are not as desireable as later Citoris with choke tubes. Field and Trap guns are not as desireable as Lightning and Superlight models. Based on the information you provided, anywhere between $550 and $1000.
No
Browning's web site has the current information.
The Browning web site has a search function that will assist you.
Try browning.com
To change the choke of the shot
Not unless it is threaded for them.
Yes
Look at the choke tubes.
If not OEM, yes
Yes, in the new A5.