[Koha] Item number confusion

[Elizabeth Lynn Edgar]

Hello,
I am an intern at a small research library for a large corporation.  One of my current assignments is to see if Koha would be a good fit for this library.  I am still in the set up phase for our test catalog and have had a few problems that I was hoping someone here might be able to point me in the right direction in answering them. According to the person who set up the server for me, we are using Koha version 3.02.00.004.

1) Our catalog records store all of the item number data for our books in the 949 field, and it does not appear that Koha likes to use the 952 field for this information.  How bad would it be for me to switch this with in Koha, or is there another way to get Koha to acknowledge the item numbers for our books?

2) We currently keep our e-books in a separate collection from the main physical collection and would like to continue doing so in Koha.  So far I have made a separate library for them.  Normally we just let the current catalog generate a generic call number/item number for them so that they are obviously different from the physical collection so we don't have people searching our shelves for an electronic book.  When I mess with the cataloging criteria for the e-book library to set it to auto generate item numbers for the e-books it seems want to change the setting to auto generate item numbers for all the library collections.  Is it possible to have one library or branch set to auto assign item numbers and another library or branch set to allow the cataloger assign the item number?

Sincerely,
Elizabeth Edgar