Would Old 1.2.7d DB overwrite New 1.3.5 DB?

When upgrading my site from 1.2.7d to 1.3.5, I did the following:

1. Fresh install of ZC v1.3.5
2. Overwrite 1.3.5 DB with 1.2.7d DB
3. Run ZC v1.3.5 DB upgrade
4. Install required mods. (some mod. required changes to DB)

All's well and good but then it dawn on me that during the upgrade, my live site has changed with new products and new/amended data. In order to preserve these changes when I switch to the 1.3.5, I have to:

A. Backup 1.2.7d DB,
B. Overwrite 1.3.5 DB with 1.2.7d DB in step A.
C. Run ZC v1.3.5 DB upgrade

Correct me if I have mistaken, when I perform Step B, whatever DB changes made in Step 4 above would be overwritten. So my question is, how can I preserve the most current DB in my live site without overwriting the DB changes made in Step 4 when I bring 1.3.5 live?

Pardon me for the long message, I hope I have provided sufficient info. for any guru out there to enlighten me. TIA.

Url below may help
http://www.zen-cart.com/wiki/index.php/Installation_-_Upgrade

Thank Misty for the link, looking thru' it, I see that it recommends progressive upgrade of the DB. However, DB changes introduces by 1.3.5 compatible mods. aren't installed in the old 1.2.7d version hence progressive DB upgrade wouldn't prevent the lost of those DB changes introduced by these new mods. :(

Most database additions for Add On functionality should be outside the realm of the core database schema and should not be affected by an upgrade.

I posted some more thoughts here (about taking notes), which may be related:
http://www.zen-cart.com/forum/showthread.php?p=274515&highlight=upgrade#post274515

Thank you so very much. I can sleep easier now. :thumbsup: