I get where you're coming from. Managing manual tax adjustments in Odoo can be a bit of a headache, right? When u manually tweak amount_tax on teh invoice, you're only affecting the current view. So basically, it doesn't really alter the core data tied to the chart of accounts.

If you need those changes to show up, you gotta dig a bit deeper. Look into changing the attributes of account.invoice.line instead. Altering the taxes per line lets you directly mess with the ledger accounts linked with each product line, making sure teh tax adjustments actually reflect in your chart of accounts.

I've faced this myself. Depending on your setup, you'd want to ensure any inv line updates sync with account entries. Also, check that your tax settings are configured to handle manual changes right - sometimes it's about tweaking settings just so.

Another method is using odoo's tax adjustment features in accounting settings. There might be a dedicated journaling method for this adjustment to properly show in GL. It needs some fine-tuning, but with the right setup, it's doable. If you aren't sure, getting a consultant on board early can really save you hassle.