This I can't do. I usually add new acquisitions as Region 1 'cos of the more complete info & better cover scan quality they have. If the title I got is R3, I just change the region in the 'disc info' tab from R1 to R3; therefore it is still recorded as US as its country of origin. That's why up until now, I have no idea how many titles for each region(1, 2 or 3) I have (p.s. I have around 1,050+ titles).
I have no idea how to customize hehe
Assuming you have 100 DVD R3. You open a new database for all your R3 collection. You can still add new acquisitions using R1 cos of the more complete info & better cover scan quality, etc...but you can change disc info tab from R1 to R3 (tho not necessary) as you can easily just rename your database to
DVD Collection R3 in order to be distinct. So, if you wana print out report on your R3 then you will just open your R3 database.
So assuming you have DVD from 3 different regions, then setup 3 separate databases to keep track of each region...in this way you'll know the exact number of DVD you have for each region.