NOTE: if you customize at code & XML level, then such customizations will be preserved and not deleted...

Thank you for your answer ! So if i import products from a csv file and I want to update Odoo later; odoo will delete these products ?? It's crazy!

No, that's NOT a case, Odoo will not delete your products. it's a different case...

Ok, I'll try to explain it otherwise: Odoo will reset some customized stuff BUT any normal records and data will be preserved...

But when I import my new accounting accounts in odoo it's just data too! As if I import products

by adding accounts you're setting up Chart Of Accounts, it's a setting, not a normal data... normal data there is journal entries/Journal Items, that are stored inside of accounts... these journal entries/items will not be touched by update...

When you installed accounting, you should be asked to choose "Accounting Package", what were your choice at that point?

Default value for "Accounting Package" is "Custom", I've leaved it unchanged, then I customized chart of accounts, that's how I've installed accounting... Now I'm tried to update and no any account were deleted... It means normally accounts are not deleted by update process. if you've chosen other thing then "Custom" for "Accounting Package" configuration, then it installs additionally some "l10n_*" module, it's quite possible that deletion is initiated from that additional module. So, most probably problem is in your local configuration in this case. I updated odoo successfully with the exactly same command as you posted.